424B5 1 e26304_fsbc-424b5.htm

Filed pursuant to Rule 424(b)(5)

Registration Statement No. 333-293089

This preliminary prospectus supplement and the accompanying prospectus are part of an effective registration statement filed with the Securities and Exchange Commission under the Securities Act of 1933, as amended, and the information in this preliminary prospectus supplement is not complete and may be changed. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell the securities described herein and are not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED JULY 22, 2026

PROSPECTUS SUPPLEMENT

(To Prospectus Dated February 9, 2026)

Shares

Common Stock

We are offering shares of our common stock, no par value per share.

Our common stock is listed on the Nasdaq Global Select Market, or Nasdaq, under the symbol “FSBC.” The last reported closing price of our common stock on Nasdaq on July 21, 2026 was $49.33 per share.

We are an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012 and, as a result, are subject to reduced public company disclosure standards. See the section entitled “Prospectus Supplement Summary—Implications of Being an Emerging Growth Company.”

Investing in our common stock involves risks. Before investing in our common stock, you should consider the information under the heading “Risk Factors” beginning on page S-14 of this prospectus supplement, on page 2 of the accompanying prospectus and under the heading “Part I. Item 1A. Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2025, as well as in each subsequently filed Quarterly Report on Form 10-Q, and other filings we may make with the U.S. Securities and Exchange Commission, or the SEC, which are incorporated herein by reference.


	Per Share	Total⁽¹⁾
Public offering price	$	$
Underwriting discounts and commissions⁽²⁾	$	$
Proceeds, before expenses, to us	$	$

(1)	Assumes no exercise of the underwriters’ option to purchase additional shares described below.

(2)	The underwriters will also be reimbursed for certain expenses incurred in this offering. See “Underwriting” for details.

We have granted the underwriters an option, exercisable not later than 30 days after the date of this prospectus supplement, to purchase up to an additional shares of common stock from us on the same terms and conditions set forth above.

None of the Securities and Exchange Commission, any state securities commission, the Federal Deposit Insurance Corporation, or the FDIC, the Board of Governors of the Federal Reserve System, or the Federal Reserve, the California Department of Financial Protection and Innovation, or the DFPI, or any other regulatory authority has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Shares of our common stock are not savings accounts, deposits or other obligations of any bank or non-bank subsidiary of Five Star Bancorp and are not insured or guaranteed by the FDIC or any other governmental agency.

Certain of our directors and their related persons or entities have indicated an interest in purchasing a portion of the shares of common stock in this offering at a price equal to the public offering price. Because this indication of interest is not a binding agreement or commitment to purchase, these persons could determine to purchase more, less or no shares in this offering or the underwriters could determine to sell more, less or no shares to these persons.

The underwriters are offering the shares of our common stock as set forth in the “Underwriting” section of this prospectus supplement. The underwriters expect to deliver the shares of common stock in book-entry form only through the facilities of The Depository Trust Company, against payment on or about , 2026.


	Bookrunner

	Keefe, Bruyette & Woods A Stifel Company

	Co-Managers

Stephens Inc.	D.A. Davidson & Co.	Raymond James	Brean Capital

Prospectus Supplement dated , 2026.

TABLE OF CONTENTS

Prospectus Supplement

ABOUT THIS PROSPECTUS SUPPLEMENT AND THE ACCOMPANYING PROSPECTUS	ii
WHERE YOU CAN FIND MORE INFORMATION	S-1
INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE	S-1
SPECIAL CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS	S-3
PROSPECTUS SUPPLEMENT SUMMARY	S-5
THE OFFERING	S-13
RISK FACTORS	S-14
USE OF PROCEEDS	S-19
CAPITALIZATION	S-20
MATERIAL U.S. FEDERAL INCOME TAX CONSIDERATIONS TO NON-U.S. HOLDERS	S-21
UNDERWRITING	S-26
LEGAL MATTERS	S-31
EXPERTS	S-31

Prospectus

ABOUT THIS PROSPECTUS	ii
WHERE YOU CAN FIND MORE INFORMATION	iii
FORWARD-LOOKING STATEMENTS	iv
THE COMPANY	1
RISK FACTORS	2
USE OF PROCEEDS	3
DESCRIPTION OF SECURITIES WE MAY OFFER	4
DESCRIPTION OF COMMON STOCK	5
DESCRIPTION OF PREFERRED STOCK	10
DESCRIPTION OF DEBT SECURITIES	13
DESCRIPTION OF DEPOSITARY SHARES	26
DESCRIPTION OF WARRANTS	29
DESCRIPTION OF PURCHASE CONTRACTS AND PURCHASE UNITS	31
DESCRIPTION OF SUBSCRIPTION RIGHTS	32
DESCRIPTION OF UNITS	33
PLAN OF DISTRIBUTION	34
LEGAL MATTERS	37
EXPERTS	37

ABOUT THIS PROSPECTUS SUPPLEMENT AND THE ACCOMPANYING PROSPECTUS

This document is composed of two parts. The first part is this prospectus supplement, which describes the specific terms of this offering of common stock, including the price, the number of shares of our common stock being offered, the risks of investing in this offering of our common stock and certain other matters relating to us and our financial condition. This prospectus supplement also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference into this prospectus supplement and the accompanying prospectus. The second part of this document is the accompanying prospectus, dated February 9, 2026, which is included as part of our shelf registration statement on Form S-3 (File No. 333-293089). That registration statement and the accompanying prospectus provide more general information about securities that we may offer from time to time, some of which may not apply to this offering. It is important for you to read and consider carefully all information contained or incorporated by reference in this prospectus supplement, the accompanying prospectus and any permitted free writing prospectuses we have authorized for use with respect to this offering before investing in our common stock. See “Where You Can Find More Information” and “Incorporation of Certain Documents by Reference” for additional information.

This prospectus supplement, or the information incorporated by reference in this prospectus supplement, may add, update or change information in the accompanying prospectus. If information in this prospectus supplement is inconsistent with the accompanying prospectus, this prospectus supplement will supersede the information in the accompanying prospectus.

In various places in this prospectus supplement and the accompanying prospectus, we refer you to sections of other documents for additional information by indicating the caption heading of the other sections. All cross-references in this prospectus supplement are to captions contained in this prospectus supplement and not in the accompanying prospectus, unless otherwise indicated.

In this prospectus supplement, “we,” “our,” “us,” “Five Star Bancorp” or “the Company” refer to Five Star Bancorp, a California corporation, and our banking subsidiary, Five Star Bank, a California state-chartered bank, unless the context indicates that we refer only to the parent company, Five Star Bancorp. In this prospectus supplement, the “Bank” refers to Five Star Bank. Unless otherwise indicated, information presented in this prospectus supplement assumes the underwriters’ option to purchase additional shares from us is not exercised.

We report our financial results in accordance with United States generally accepted accounting principles. All financial data in this prospectus supplement for the three and six months ended June 30, 2026 is preliminary. These preliminary results are not a comprehensive statement of our financial position for the three and six months ended June 30, 2026 and are based on information available as of the date of this prospectus supplement. The actual amounts that we report will be subject to any final adjustments that may be made prior to the time our financial results for the three and six months ended June 30, 2026 are finalized and filed with the SEC in our Quarterly Report on Form 10-Q for the quarter ended June 30, 2026.

The preliminary results included in this prospectus supplement have been prepared by, and are the responsibility of, our management. Baker Tilly US, LLP has not audited, reviewed, examined, compiled, or applied agreed upon procedures with respect to the preliminary results. Accordingly, Baker Tilly US, LLP does not express an opinion or any other form of assurance with respect thereto.

Neither the Company nor the underwriters have authorized anyone to provide you with any information other than that contained or incorporated by reference in this prospectus supplement, the accompanying prospectus or in any free writing prospectus prepared by or on behalf of, the Company, or to which the Company has referred you. Neither the Company nor the underwriters take any responsibility for, or can provide any assurance as to the reliability of, any information that others may give you. If any information in this prospectus supplement is inconsistent with the accompanying prospectus or any document incorporated by reference in this prospectus supplement or the accompanying prospectus, you should rely on the information in this prospectus supplement. You should not assume that the information provided in this prospectus supplement, the accompanying prospectus or the documents incorporated by reference in this prospectus supplement and in the accompanying prospectus is accurate as of any date other than the date of this prospectus supplement or the date of the document in which that information is contained. Our business, financial condition, liquidity, results of operations and prospects may have changed since the date of any document in which such information is contained.

Neither the Company nor the underwriters are offering to sell nor seeking an offer to buy our common stock in any jurisdiction where such offers and sales are not permitted. The distribution of this prospectus supplement and the accompanying prospectus and the offering of our common stock in certain jurisdictions may be restricted by law.

Persons outside the United States who come into possession of this prospectus supplement and the accompanying prospectus must inform themselves about and observe any restrictions relating to the offering of our common stock and the distribution of this prospectus supplement and the accompanying prospectus outside the United States. This prospectus supplement and the accompanying prospectus do not constitute, and may not be used for or in connection with, an offer or solicitation by any person in any jurisdiction in which such offer or solicitation is not authorized or in which the person making such offer or solicitation is not authorized or is not qualified to do so or to any person to whom it is unlawful to make such offer or solicitation, and this prospectus supplement and the accompanying prospectus may not be delivered to any person to whom it is unlawful to make such offer or solicitation. See “Underwriting” in this prospectus supplement.

iii

WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and current reports, proxy statements and other information with the SEC. Our filings with the SEC are also available to the public through the SEC’s website at www.sec.gov.

Our annual, quarterly and current reports and any amendments to those reports are also available over the Internet on our website at www.fivestarbank.com. All internet addresses provided in this prospectus supplement or the accompanying prospectus are for informational purposes only and are not intended to be hyperlinks. In addition, the information on, or accessible through, our website, or any other website described herein, is not a part of, and is not incorporated or deemed to be incorporated by reference in, this prospectus supplement or the accompanying prospectus or other offering materials.

We have filed a shelf registration statement (File No. 333-293089) with the SEC registering the offering of various of our securities, including the shares of our common stock offered by this prospectus supplement and the accompanying prospectus. This prospectus supplement and the accompanying prospectus are part of that registration statement. The registration statement may contain additional information that may be important to you. Statements contained in this prospectus supplement and the accompanying prospectus as to the contents of any contract or other document referred to, or incorporated by reference, in this prospectus supplement and the accompanying prospectus are not necessarily complete and, where that contract or document is an exhibit to the registration statement, each statement is qualified in all respects by the exhibit to which the reference relates. You may obtain from the SEC copies of the registration statement and the related exhibits that we filed with the SEC.

INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

The SEC’s rules allow us to incorporate by reference information into this prospectus supplement and the accompanying prospectus. This means that we can disclose important information to you by referring you to another document. Any information incorporated by reference into this prospectus supplement and the accompanying prospectus is considered a part of the information contained herein and therein. We are incorporating by reference in this prospectus supplement, and have incorporated by reference in the accompanying prospectus, the documents listed below, which we have already filed with the SEC, and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, as amended, or the Exchange Act, except in each case as to any portion of any report or document that is deemed furnished to the SEC and not deemed filed under such provisions:

our Annual Report on Form 10-K for the year ended December 31, 2025, filed with the SEC on February 27, 2026;

our Quarterly Report on Form 10-Q for the quarter ended March 31, 2026, filed with the SEC on May 7, 2026;

the information specifically incorporated by reference into our Annual Report on Form 10-K for the year ended December 31, 2025 from our Definitive Proxy Statement on Schedule 14A, filed with the SEC on March 30, 2026;

our Current Report on Form 8-K, filed with the SEC on May 28, 2026; and

the description of our common stock contained in Exhibit 4.4 to our Annual Report on Form 10-K for the year ended December 31, 2021, filed with the SEC on February 25, 2022.

The information contained in this prospectus supplement and the accompanying prospectus will be updated and supplemented by the information contained in the filings we make with the SEC in the future and that are incorporated by reference into this prospectus supplement and the accompanying prospectus as described above. The information contained in those future filings will be considered to be part of this prospectus supplement and the accompanying prospectus and will automatically update and supersede, as appropriate, the information contained in this prospectus supplement and the accompanying prospectus and contained in the filings previously filed with the SEC that are incorporated by reference into this prospectus supplement and the accompanying prospectus.

S-1

Upon written or oral request, we will provide, without charge, to each person to whom a copy of this prospectus supplement and the accompanying prospectus is delivered a copy of the documents incorporated by reference into this prospectus supplement and the accompanying prospectus. You may request a free copy of these filings by writing or telephoning us at the following address:

Five Star Bancorp

Attention: Heather Luck

3100 Zinfandel Drive, Suite 100

Rancho Cordova, California 95670

Telephone: (916) 626-5008

S-2

SPECIAL CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus, and the documents incorporated by reference herein and therein include “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. These forward-looking statements represent plans, estimates, objectives, goals, guidelines, expectations, intentions, projections, and statements of our beliefs concerning future events, business plans, objectives, expected operating results, and the assumptions upon which those statements are based. Forward-looking statements include, without limitation, any statement that may predict, forecast, indicate, or imply future results, performance, or achievements, and are typically identified with words such as “may,” “could,” “should,” “will,” “would,” “believe,” “anticipate,” “estimate,” “expect,” “aim,” “intend,” “plan,” or words or phrases of similar meaning. To the extent that this discussion describes prior performance, the descriptions relate only to the periods listed, which may not be indicative of our future financial outcomes. We caution that the forward-looking statements are based largely on our expectations and are subject to a number of known and unknown risks and uncertainties that are subject to change based on factors which are, in many instances, beyond our control. Such forward-looking statements are based on various assumptions (some of which may be beyond our control) and are subject to risks and uncertainties, which change over time, and other factors which could cause actual results to differ materially from those currently anticipated. Such risks and uncertainties include, but are not limited to:

risks related to the concentration of our business in California, and specifically within Northern California, including risks associated with any downturn in the real estate sector;

changes in market interest rates that affect the pricing of our loans and deposits, our net interest income, and our borrowers’ ability to repay loans;

changes in the U.S. economy, including an economic slowdown, recession, inflation, deflation, tariffs, housing prices, employment levels, rate of growth, and general business conditions;

uncertain market conditions and economic trends nationally, regionally, and particularly in Northern California and California;

the soundness of other financial institutions and the impacts related to or resulting from bank failures and other economic and industry volatility, including increased regulatory requirements and costs and potential impacts to macroeconomic conditions;

the impact of recent and future legislative and regulatory changes, including changes in banking, securities, and tax laws and regulations and their application by our regulators;

the effects of increased competition from a wide variety of local, regional, national, and other providers of financial and investment services;

the risks associated with our loan portfolios, and specifically with our commercial real estate loans;

our ability to maintain adequate liquidity and to maintain capital necessary to fund our growth strategy and operations and to satisfy minimum regulatory capital levels;

risks related to our strategic focus on lending to small to medium-sized businesses;

the sufficiency of the assumptions and estimates we make in establishing reserves for potential credit losses and the value of loan collateral and securities;

our level of nonperforming assets and the costs associated with resolving problem loans, if any;

our ability to comply with various governmental and regulatory requirements applicable to financial institutions, including supervisory actions by federal and state banking agencies;

governmental monetary and fiscal policies, including the policies of the Federal Reserve;

S-3

risks associated with unauthorized access, cybersecurity breaches, cyber-crime, and other threats and disruptions to data security;

our ability to implement, maintain, and improve an effective risk management framework, disclosure controls and procedures, and internal controls over financial reporting;

our ability to adopt and successfully integrate new initiatives or technologies into our business in a strategic manner;

our ability to attract and retain executive officers and key employees and their customer and community relationships;

the impact of any future U.S. federal government shutdown and uncertainty regarding the U.S. federal government’s debt limit and credit rating;

the occurrence or impact of climate change or natural or man-made disasters or calamities, such as wildfires, droughts, mudslides, floods, and earthquakes, and particularly in California, and specifically Northern California;

changes in and impact of local, regional, and global business, economic, and political conditions and geopolitical events, such as pandemics, civil unrest, wars, and acts of terrorism;

our use of the net proceeds from this offering; and

other factors that are discussed in the section entitled “Risk Factors.”

The foregoing factors could cause results or performance to materially differ from those expressed in our forward-looking statements, should not be considered exhaustive, and should be read together with other cautionary statements that are included in this prospectus supplement, in the accompanying prospectus and in the documents incorporated herein by reference, including in our Annual Report on Form 10-K for the year ended December 31, 2025, as well as in each subsequently filed Quarterly Report on Form 10-Q, and other filings we may make with the SEC, copies of which are available from us at no charge. New risks and uncertainties may emerge from time to time, and it is not possible for us to predict their occurrence or how they will affect us. If one or more of the factors affecting our forward-looking information and statements proves incorrect, then our actual results, performance, or achievements could differ materially from those expressed in, or implied by, forward-looking information and statements contained in this prospectus supplement. Therefore, we caution you not to place undue reliance on our forward-looking information and statements. We disclaim any duty to revise or update the forward-looking statements, whether written or oral, to reflect actual results or changes in the factors affecting the forward-looking statements, except as specifically required by law.

S-4

PROSPECTUS SUPPLEMENT SUMMARY

The following summary provides a brief overview of certain information appearing elsewhere in this prospectus supplement and the documents incorporated by reference herein, which are described under “Incorporation of Certain Documents by Reference.” Because it is a summary, it does not contain all the information that may be important to you. Before making an investment decision, you should read this entire prospectus supplement and the accompanying prospectus carefully, including the section entitled “Risk Factors” in this prospectus supplement, and the documents incorporated by reference herein and in the accompanying prospectus, including the financial statements and the accompanying notes contained in such documents.

Five Star Bancorp

Headquartered in the greater Sacramento metropolitan area of California, Five Star Bancorp is a bank holding company that operates through its wholly owned subsidiary, Five Star Bank, a California state-chartered non-member bank. We provide a broad range of banking products and services to small and medium-sized businesses, professionals, and individuals primarily in Northern California through nine branch offices, with a tenth branch opening in July 2026. Our mission is to strive to become the top business bank in all markets we serve through exceptional service, deep connectivity, and customer empathy. We are dedicated to serving real estate, agricultural, faith-based, and small to medium-sized enterprises. We aim to consistently deliver value that meets or exceeds the expectations of our shareholders, customers, employees, business partners, and community. We refer to our mission as “purpose-driven and integrity-centered banking.” At March 31, 2026, we had total assets of $5.0 billion, total loans held for investment of $4.2 billion, and total deposits of $4.5 billion.

We are regulated by the FDIC, the Federal Reserve, the DFPI, and other regulatory agencies. See the section entitled “Supervision and Regulation” in our Annual Report on Form 10-K for the year ended December 31, 2025 for more information.

Our principal executive office is located at 3100 Zinfandel Drive, Suite 100, Rancho Cordova, CA 95670, and our telephone number is (916) 626-5000. Our common stock is traded on Nasdaq under the symbol “FSBC”. Additional information about us and our subsidiaries may be found in the documents incorporated by reference into this prospectus supplement. See “Where You Can Find More Information.”

Recent Developments

Financial Highlights for the Second Quarter 2026

On July 22, 2026, we reported unaudited preliminary consolidated financial results for the quarter ended June 30, 2026, including the below.

The following information is only a summary and is not intended to be a comprehensive statement of the Company’s financial results. The following financial results are preliminary and unaudited and may be revised as a result of management’s further review of our results. Our independent registered public accounting firm, Baker Tilly US, LLP, has not audited, reviewed, compiled or performed any procedures on the following preliminary financial information. During the course of the preparation of our quarterly financial statements and related notes, we may identify items that would require the Company to make adjustments to the preliminary financial information presented below. Accordingly, these preliminary results should not be viewed as a substitute for financial statements prepared in accordance with accounting principles generally accepted in the United States, and you should not place undue reliance on these preliminary results. We assume no duty to update these preliminary results, except as required by law. The following should be read in conjunction with our consolidated financial statements and related notes, as well as management’s discussion and analysis of financial condition and results of operations, in our filings with the SEC that are incorporated by reference herein and the sections entitled “Cautionary Note Regarding Forward-Looking Statements” and “Risk Factors” in this prospectus supplement and similar sections in filings with the SEC that are incorporated by reference herein. Financial statements as of and for the quarter ended June 30, 2026 will be included in our Quarterly Report on Form 10-Q to be filed with the SEC.

S-5

We reported net income of $19.4 million for the three months ended June 30, 2026, as compared to $18.6 million for the three months ended March 31, 2026 and $14.5 million for the three months ended June 30, 2025.

The following presents highlights of the Company’s unaudited preliminary consolidated financial results and other developments for the Company for the periods indicated:

Financial Results (unaudited)

	Three months ended
(in thousands, except per share and share data)	June 30, 2026			March 31, 2026			June 30, 2025
Selected operating data:
Net interest income	$	46,083		$	43,457		$	36,515
Provision for credit losses		2,250			2,675			2,500
Non-interest income		1,872			1,643			1,810
Non-interest expense		19,616			17,394			15,726
Pre-tax income		26,089			25,031			20,099
Provision for income taxes		6,690			6,410			5,591
Net income	$	19,399		$	18,621		$	14,508
Earnings per common share:
Basic	$	0.91		$	0.87		$	0.68
Diluted	$	0.91		$	0.87		$	0.68
Weighted average basic common shares outstanding		21,273,902			21,253,085			21,225,831
Weighted average diluted common shares outstanding		21,338,903			21,313,078			21,269,265
Shares outstanding at end of period		21,402,864			21,376,153			21,360,991
Performance and other financial ratios:
Return on average assets (“ROAA”)		1.49	%		1.55	%		1.37	%
Return on average equity (“ROAE”)		16.67	%		16.73	%		14.17	%
Tangible book value per share⁽¹⁾	$	22.14		$	21.45		$	19.51
Net interest margin		3.63	%		3.70	%		3.53	%
Average loan yield		6.08	%		6.07	%		6.09	%
Average cost of interest-bearing deposits		2.89	%		2.88	%		3.31	%
Average cost of total deposits		2.16	%		2.13	%		2.46	%
Total cost of funds⁽²⁾		2.23	%		2.20	%		2.53	%
Efficiency ratio		40.91	%		38.57	%		41.03	%

(1)	Tangible book value per share is equal to book value per share calculated in accordance with U.S. generally accepted accounting principles.

(2)	Total cost of funds reflects the average cost of all funding sources, including both interest-bearing and non-interest-bearing deposits and borrowings.

S-6

Balance Sheet Summary (unaudited)

(in thousands)	June 30, 2026			March 31, 2026			December 31, 2025
Selected financial condition data:
Total assets	$	5,377,062		$	5,031,751		$	4,754,861
Cash and cash equivalents		685,074			644,359			506,851
Total loans held for investment		4,519,681			4,213,393			4,074,929
Total investments		92,719			93,850			96,889
Total liabilities		4,903,291			4,573,232			4,309,029
Total deposits		4,799,383			4,469,353			4,201,084
Total securities to interest-earning assets		1.77	%		1.91	%		2.09	%
Subordinated notes, net		74,114			74,077			74,041
Total shareholders’ equity		473,771			458,519			445,832

Insured and collateralized deposits were approximately $3.2 billion, representing 65.80% of total deposits, as of June 30, 2026, as compared to 65.55% as of March 31, 2026. Net uninsured and uncollateralized deposits were approximately $1.6 billion as of June 30, 2026, increasing from $1.5 billion at March 31, 2026.

Non-wholesale deposit balances constituted 94.79% of total deposits as of June 30, 2026, as compared to 91.43% as of March 31, 2026. Deposit relationships of greater than $5 million represented 63.88% of total deposits as of June 30, 2026, as compared to 60.67% as of March 31, 2026, and had an average age of approximately 7.39 years as of June 30, 2026, as compared to 7.98 years as of March 31, 2026.

Total deposits as of June 30, 2026 were $4.8 billion, an increase of $330.0 million, or 7.38%, from March 31, 2026, comprised of an increase in interest-bearing deposits, partially offset by a decrease in non-interest-bearing deposits. Non-interest-bearing deposits represented 27.6% of total deposits as of March 31, 2026, and declined to 24.5% of total deposits as of June 30, 2026. See below for further detail on our interest-bearing deposits.

Annualized deposit growth was 29.5% in the second quarter of 2026. Annualized non-time deposit growth was 47.5% in the second quarter of 2026. Annualized loan growth was 29.1% in the second quarter of 2026.

Total liquidity (consisting of cash and cash equivalents as well as unused and immediately available borrowing capacity as set forth below) was approximately $2.3 billion as of June 30, 2026, as compared to $2.2 billion at March 31, 2026.

	June 30, 2026
(in thousands)	Line of Credit		Letters of Credit Issued		Borrowings		Available
Federal Home Loan Bank of San Francisco (“FHLB”) advances	$	1,629,065	$	1,297,500	$	—	$	331,565
Federal Reserve Discount Window		1,074,577		—		—		1,074,577
Correspondent bank lines of credit		185,000		—		—		185,000
Cash and cash equivalents		—		—		—		685,074
Total	$	2,888,642	$	1,297,500	$	—	$	2,276,216

Other comprehensive income was $0.7 million during the three months ended June 30, 2026. Unrealized losses, net of tax effect, on available-for-sale securities were $9.4 million as of June 30, 2026. Total carrying value of held-to-maturity and available-for-sale securities represented 0.04% and 1.72% of total interest-earning assets, respectively, as of June 30, 2026.

S-7

The Company’s Tier 1 leverage ratio was 9.21% and 9.56% as of June 30, 2026 and March 31, 2026, respectively. The Company’s common equity Tier 1 capital to risk weighted assets and Tier 1 capital to risk weighted assets were both 9.98% and 10.45% as of June 30, 2026 and March 31, 2026, respectively. The Company’s total capital to risk weighted assets was 12.51% and 13.17% as of June 30, 2026 and March 31, 2026, respectively.

Net Interest Income and Net Interest Margin

The following is a summary of the components of net interest income for the periods indicated:

	Three months ended
(in thousands)	June 30, 2026			March 31, 2026			June 30, 2025
Interest and fee income	$	72,327		$	67,347		$	60,580
Interest expense		26,244			23,890			24,065
Net interest income	$	46,083		$	43,457		$	36,515
Net interest margin		3.63	%		3.70	%		3.53	%

Loans by Type

The following table provides loan balances, excluding deferred loan fees, by type as of the dates shown:

(in thousands)	June 30, 2026			March 31, 2026
Real estate:
Commercial	$	3,597,173		$	3,421,902
Commercial land and development		2,507			2,519
Commercial construction		124,053			108,179
Residential construction		21,809			17,808
Residential		41,874			43,195
Farmland		59,900			61,090
Commercial:
Secured		258,736			243,140
Unsecured		41,263			41,971
Consumer and other		374,614			275,891
Net deferred loan fees		(2,248	)		(2,302	)
Total loans held for investment	$	4,519,681		$	4,213,393

S-8

Interest-bearing Deposits

The following table provides interest-bearing deposit balances by type as of the dates shown:

(in thousands)	June 30, 2026		March 31, 2026
Interest-bearing transaction accounts	$	500,256	$	349,138
Savings accounts		147,435		141,961
Money market accounts		2,669,295		2,291,215
Time accounts		307,991		454,343
Total interest-bearing deposits	$	3,624,977	$	3,236,657

Asset Quality

At June 30, 2026, the Company’s allowance for credit losses was $47.3 million, as compared to $44.4 million at December 31, 2025. The $2.9 million increase in the allowance is due to a $4.6 million provision for credit losses recorded during the six months ended June 30, 2026, partially offset by net charge-offs of $1.6 million, primarily attributable to commercial and industrial loans, during the same period. The Company’s nonperforming loans increased from $3.1 million to $13.4 million between December 31, 2025 and June 30, 2026, increasing the ratio of nonperforming loans to loans held for investment from 0.08% at December 31, 2025 to 0.30% at June 30, 2026. This increase was due to one Community Reinvestment Act loan that was placed on non-accrual status during the period.

Loans designated as watch increased from $101.9 million to $154.6 million between December 31, 2025 and June 30, 2026. Loans designated as special mention increased from $37.5 million to $44.9 million between December 31, 2025 and June 30, 2026. Loans designated as substandard decreased from $22.3 million to $20.3 million between December 31, 2025 and June 30, 2026. There were no loans with doubtful risk grades at June 30, 2026 or December 31, 2025.

A summary of the allowance for credit losses by loan class is as follows:

	June 30, 2026		December 31, 2025
(in thousands)	Amount		Amount
Real estate:
Commercial	$	28,371	$	25,219
Commercial land and development		90		56
Commercial construction		4,444		4,050
Residential construction		533		213
Residential		419		362
Farmland		468		467
		34,325		30,367
Commercial:
Secured		9,594		11,204
Unsecured		486		482
		10,080		11,686
Consumer and other		2,930		2,356
Total allowance for credit losses	$	47,335	$	44,409

S-9

Non-interest Income

The following table presents the key components of non-interest income for the periods indicated:

	Three months ended
(in thousands)	June 30, 2026		March 31, 2026			June 30, 2025
Service charges on deposit accounts	$	122	$	135		$	196
Gain on sale of loans		—		—			119
Loan-related fees		679		1,265			468
FHLB stock dividends		191		762			325
Earnings on bank-owned life insurance		265		225			220
Other income		615		(744	)		482
Total non-interest income	$	1,872	$	1,643		$	1,810

Non-interest Expense

The following table presents the key components of non-interest expense for the periods indicated:

	Three months ended
(in thousands)	June 30, 2026		March 31, 2026		June 30, 2025
Salaries and employee benefits	$	11,421	$	11,430	$	8,910
Occupancy and equipment		873		829		657
Data processing and software		1,709		1,551		1,508
FDIC insurance		585		545		470
Professional services		952		926		918
Advertising and promotional		959		744		865
Loan-related expenses		304		247		423
Other operating expenses		2,813		1,122		1,975
Total non-interest expense	$	19,616	$	17,394	$	15,726

Provision for Income Taxes

Provision for income taxes increased by $0.3 million, or 4.37%, for the three months ended June 30, 2026, as compared to the three months ended March 31, 2026. The effective tax rates were 25.64% and 25.61% for the three months ended June 30, 2026 and March 31, 2026, respectively. Provision for income taxes increased by $1.1 million, or 19.66%, for the three months ended June 30, 2026, as compared to the three months ended June 30, 2025. The effective tax rates were 25.64% and 27.82% for the three months ended June 30, 2026 and June 30, 2025, respectively.

Dividend

The Company’s Board of Directors declared, and the Company subsequently paid, a cash dividend of $0.25 per share during the three months ended June 30, 2026. The Company’s Board of Directors declared an additional cash dividend of $0.25 per share on July 16, 2026, which the Company expects to pay on August 10, 2026 to shareholders of record as of August 3, 2026.

Franchise Expansion

Talent Acquisition

As of the date of this prospectus supplement, the Company had 49 business development officers, an increase of seven year-to-date, nine since June 30, 2025 and 28 since December 31, 2022.

S-10

Bay Area Expansion

The Bank’s Downtown San Francisco branch opened in September 2024 and Walnut Creek branch opened in September 2025. The Bank hired 34 additional employees since early 2024 to support the expansion, including four key hires in Palo Alto announced on July 15, 2026. Bay Area deposits increased by $215 million to $672 million and loans increased by $342 million to $715 million, each from June 30, 2025 to June 30, 2026.

Southern California Expansion

The Bank entered the Southern California market in September 2024 and has since grown to an 11-person team as of the date of this prospectus supplement. The Bank opened its Newport Beach administrative office in September 2025.

Food, Agribusiness and Diversified Industries

The Bank entered the food, agribusiness and diversified industries market in May 2025, growing to a seven-person team as of the date of this prospectus supplement, and opened its Lodi branch in July 2026.

Implications of Being an Emerging Growth Company

We qualify as an “emerging growth company” under the Jumpstart Our Business Startups Act of 2012, or the JOBS Act. An emerging growth company may take advantage of reduced reporting requirements and is relieved of certain other significant requirements that are otherwise generally applicable to public companies. Among other factors, as an emerging growth company:

we may present only two years of audited financial statements and discuss only our results of operations for two years in “Management’s Discussion and Analysis of Financial Condition and Results of Operations” in our Annual and Quarterly Reports on Forms 10-K and 10-Q, respectively;

we are exempt from the requirement to provide an opinion from our auditors on the design and operating effectiveness of our internal control over financial reporting pursuant to the Sarbanes-Oxley Act of 2002, as amended;

we may choose not to comply with any new requirements adopted by the Public Company Accounting Oversight Board requiring mandatory audit firm rotation or a supplement to the auditor’s report providing additional information about the audit and our audited financial statements;

we are permitted to provide less extensive disclosure regarding our executive compensation arrangements pursuant to the rules applicable to smaller reporting companies, which means we are not required to include a compensation discussion and analysis and other disclosures regarding our executive compensation in our Annual Reports on Form 10-K; and

we are not required to hold nonbinding advisory votes on executive compensation or golden parachute arrangements.

We have taken advantage of some of these provisions since our initial public offering and may continue to take advantage of these provisions until we cease to qualify as an emerging growth company on December 31, 2026. We have elected to adopt the reduced disclosure requirements described above regarding the number of periods for which we are providing audited financial statements and selected financial data, and our executive compensation arrangements. In addition, we take advantage of the reduced reporting and other requirements under the JOBS Act with respect to the periodic reports we file with the SEC and proxy statements that we use to solicit proxies from our shareholders. Accordingly, the information contained herein may be different than the information you receive from other public companies in which you invest.

S-11

The JOBS Act exempts emerging growth companies from compliance with new or revised financial accounting standards until private companies (that is, those that have not had a registration statement declared effective under the Securities Act of 1933, as amended, or the Securities Act, or do not have a class of securities registered under the Exchange Act) are required to comply with the new or revised financial accounting standards. The JOBS Act provides that a company can elect to opt out of this extended transition period and comply with the requirements that apply to non-emerging growth companies, but any such election to opt out is irrevocable. We have elected not to opt out of such extended transition period, which means that when a standard is issued or revised and it has different application dates for public or private companies, we, as an emerging growth company, can adopt the new or revised standard at the time private companies adopt the new or revised standard. As such, our consolidated financial statements may not be comparable with those of a public company that is not an emerging growth company, or those of a public company that is an emerging growth company that has opted out of using the extended transition period, because of the potential differences in accounting standards used.

S-12

THE OFFERING

Issuer		Five Star Bancorp
Shares of common stock offered by us		shares (or shares if the underwriters exercise in full their option to purchase additional shares).
Shares of common stock to be outstanding after the offering		shares (or shares if the underwriters exercise in full their option to purchase additional shares).
Public offering price per share		$
Use of proceeds		We intend to use the net proceeds from this offering for general corporate purposes and to support our continued growth, including through investments in the Bank to pursue growth opportunities, and for working capital.
Indication of interest		Certain of our directors and their related persons or entities have indicated an interest in purchasing a portion of the shares of common stock in this offering at a price equal to the public offering price. Because this indication of interest is not a binding agreement or commitment to purchase, these persons could determine to purchase more, less or no shares in this offering or the underwriters could determine to sell more, less or no shares to these persons.
Risk factors		You should carefully read and consider the information set forth under the heading “Risk Factors” beginning on page S-14 in this prospectus supplement and the accompanying prospectus, and under the heading “Part I. Item 1A. Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2025, as well as in each subsequently filed Quarterly Report on Form 10-Q, and other filings we may make with the SEC, which are incorporated by reference into this prospectus supplement, along with all other information included in and incorporated by reference into this prospectus supplement and the accompanying prospectus, before deciding to invest in our common stock.
Lock-up agreements		We and each of our executive officers and directors have agreed with the underwriters not to engage in certain transactions in our securities during the Lock-Up Period (as defined below) without the consent of the underwriters. See “Underwriting—Lock-Up Agreements” in this prospectus supplement.
Listing and trading symbol		Our common stock is traded on Nasdaq under the symbol “FSBC”.

Unless otherwise noted, references in this prospectus supplement to the number of shares of our common stock outstanding after this offering are based on 21,376,153 shares of our common stock issued and outstanding as of March 31, 2026. Except as otherwise indicated, the information in this prospectus supplement:

includes 116,103 unvested restricted stock awards outstanding as of March 31, 2026;

includes 23,110 unvested performance-based restricted stock awards outstanding as of March 31, 2026;

excludes 1,353,100 shares of our common stock reserved for issuance under the Five Star Bancorp 2021 Equity Incentive Plan as of March 31, 2026;

excludes 26,711 unvested restricted stock awards granted after March 31, 2026;

excludes 25,790 performance-based restricted stock awards granted after March 31, 2026;

assumes no exercise of the underwriters’ option to purchase additional shares of our common stock; and

does not attribute to any director or their related persons or entities any purchases of shares of our common stock in this offering.

S-13

RISK FACTORS

An investment in our common stock involves a significant degree of risk. The material risks and uncertainties that management believes affect us are described below. Before you decide to invest in our common stock, you should carefully read and consider all of the information contained in this prospectus supplement, including the risks and uncertainties described below and under “Special Cautionary Note Regarding Forward-Looking Statements” in this prospectus supplement, and the other documents incorporated by reference into this prospectus supplement, including the risks and uncertainties described under “Risk Factors” in the accompanying prospectus and our Annual Report on Form 10-K for the year ended December 31, 2025, as well as in each subsequently filed Quarterly Report on Form 10-Q, and other filings we may make with the SEC. Any of these risks, if they are realized, could have an adverse effect on our business, financial condition and results of operations, and consequently, the value of our common stock. In any such case, you could lose all or a portion of your original investment. Further, additional risks and uncertainties not currently known to us or that we currently believe to be immaterial may also adversely affect us. This prospectus supplement also contains forward-looking statements that involve risks and uncertainties. See the section entitled “Special Cautionary Note Regarding Forward-Looking Statements.”

Risks Related to an Investment in Our Common Stock and the Offering

Future sales or the possibility of future sales of our common stock could depress the market price of our common stock.

Our amended and restated articles of incorporation, or our articles of incorporation, authorize us to issue up to 100,000,000 shares of common stock. Following the completion of this offering, we will have issued and outstanding shares of our common stock (or shares if the underwriters exercise their option to purchase additional shares in full), a significant portion of which will be freely transferable without restriction or further registration under the Securities Act. We and our executive officers and our directors holding, in the aggregate, 4,657,677 shares of our common stock as of March 31, 2026 (representing approximately 21.79% of our outstanding shares of common stock as of such date), have agreed not to sell any shares of our common stock for a period of 90 days from the date of this prospectus supplement, or the Lock-Up Period, subject to certain exceptions. See the section entitled “Underwriting.” Following the expiration of the Lock-Up Period, all of these shares will be eligible for resale under Rule 144 of the Securities Act, subject to any applicable holding period requirements and volume limitations. In addition, the underwriters, at any time and without notice, may release all or any portion of the common stock subject to such lock-up restrictions. The remaining shares of our common stock outstanding prior to this offering are not subject to lock-up agreements and they may be freely resold at any time, subject to the restrictions described in this prospectus supplement, if applicable, for affiliate holders. The shares of our common stock being offered and sold in this offering will also generally be available for resale into the public markets. See the section entitled “Underwriting.”

We may also issue additional shares in the future for various purposes without any action or approval by our shareholders, and these shares, once issued, will be available for sale into the public market, subject to the restrictions described in this prospectus supplement, if applicable, for affiliate holders. The market price for our common stock may decline significantly when the restrictions on resale by our existing shareholders lapse. Actual or anticipated issuances or sales of substantial additional amounts of our common stock following this offering could cause the market price of our common stock to decline significantly and make it more difficult for us to sell equity or equity-related securities in the future on favorable terms, or at all. We cannot predict the size of future issuances of our common stock or the effect, if any, that future issuances and sales of our common stock will have on the market price of our common stock. Sales of substantial amounts of our common stock, or the perception that such sales could occur, may adversely affect prevailing market prices for our common stock. Further, a decline in the market price of our common stock might impede our ability to raise capital through the issuance of additional common stock or other equity securities.

S-14

The market price of our common stock may be volatile, and we may not be able to meet investor or analyst expectations. You may not be able to resell your shares at or above the price you paid and may lose part or all of your investment as a result.

Volatility in the market price of our common stock may negatively impact the price at which our common stock may be sold and may also negatively impact the timing of any sale. The market price of our common stock may continue to fluctuate widely in response to a variety of factors including the risk factors described herein and, among other things:

actual or anticipated variations in quarterly or annual operating results, financial conditions, or credit quality;

changes in business or economic conditions;

changes in accounting standards, policies, guidance, interpretations, or principles;

changes in recommendations or research reports about us or the financial services industry in general published by securities analysts;

changes in financial estimates or publication of research reports and recommendations by financial analysts or actions taken by rating agencies with respect to us or other financial institutions;

news reports relating to trends, concerns, and other issues in the financial services industry;

perceptions in the marketplace regarding us or our competitors;

sudden increases in the demand for our common stock, including as a result of any “short squeezes”;

significant acquisitions or business combinations, strategic partnerships, joint ventures, or capital commitments by or involving us or our competitors;

additional investments from third parties;

additions or departures of key personnel;

future sales or issuance of additional shares of our common stock;

changes or proposed changes in laws or regulations, or differing interpretations thereof, affecting our business, or enforcement of these laws or regulations; or

geopolitical conditions or natural or man-made disasters.

In particular, the realization of any of the risks described in this section or under the heading “Part I. Item 1A. Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2025, as well as in each subsequently filed Quarterly Report on Form 10-Q, and other filings we may make with the SEC, which are incorporated herein by reference, could have an adverse effect on the market price of our common stock and cause the value of your investment to decline. In addition, the stock market in general has experienced extreme volatility that has often been unrelated to the operating performance of particular companies. These broad market fluctuations may adversely affect the market price of our common stock over the short, medium or long term, regardless of our actual performance. In the past, following periods of volatility in the market price of a company’s securities, shareholders have often instituted securities class action litigation. If we were to be involved in a class action lawsuit, it could divert the attention of our senior management and could adversely affect our business, financial condition and results of operations.

S-15

If securities or industry analysts do not publish research or publish inaccurate or unfavorable research about our business, or change their recommendations regarding our common stock or if our operating results do not meet their expectations, the market price of our common stock and trading volume could decline.

The trading market for our common stock depends in part on the research and reports that securities or industry analysts publish about us or our business. If one or more of the analysts who covers us downgrades our stock or publishes inaccurate or unfavorable research about our business, or our operating results do not meet their expectations, either absolutely or relative to our competitors, the market price of our common stock would likely decline. If one or more of these analysts cease coverage of us or fail to publish reports on us regularly, we could lose visibility in the financial markets, which in turn could cause the market price of our common stock or trading volume to decline. If we fail to meet the expectations of analysts for our operating results, the market price of our common stock would likely decline. If one or more of these analysts cease coverage of us or fails to publish reports on us regularly, demand for our stock could decrease, which could cause the market price of our common stock and trading volume to decline.

We depend on the Bank for cash flow, and the Bank’s ability to make cash distributions is restricted, which could impact our ability to satisfy our obligations.

We are a bank holding company with no material activities other than activities incidental to holding the common stock of the Bank. Our principal source of funds to pay distributions on our common stock and service any of our obligations, other than further issuances of securities, is dividends received from the Bank. The holding company, Five Star Bancorp, is a legal entity separate and distinct from the Bank. Furthermore, the Bank is not obligated to pay dividends to us, and any dividends paid to us would depend on the earnings or financial condition of the Bank, various business considerations, and applicable law and regulation. As is generally the case for banking institutions, the profitability of the Bank is subject to the fluctuating cost and availability of money, changes in interest rates, and economic conditions in general. In addition, various federal and state statutes and regulations limit the amount of dividends that the Bank may pay to us without regulatory approval.

We may not pay dividends on our common stock in the future, and our ability to pay dividends is subject to certain restrictions.

Holders of our common stock are entitled to receive only such dividends as our board of directors may declare out of funds legally available for such payments. Our board of directors may, in its sole discretion, change the amount or frequency of dividends or discontinue the payment of dividends entirely. In addition, we are a bank holding company, and our ability to declare and pay dividends is dependent on federal regulatory considerations, including the guidelines of the Federal Reserve regarding capital adequacy and dividends. It is the policy of the Federal Reserve that bank holding companies should generally pay dividends on common stock only out of earnings, and only if prospective earnings retention is consistent with the organization’s expected future needs, asset quality, and financial condition, and that bank holding companies should inform and consult with the Federal Reserve in advance of declaring and paying a dividend that exceeds earnings for the period for which the dividend is being paid.

The holders of our debt obligations and preferred stock will have priority over our common stock with respect to payment in the event of liquidation, dissolution or winding up and with respect to the payment of interest and dividends.

In any liquidation, dissolution or winding up of the Company, our common stock would rank below all claims of debt holders against us as well as any preferred stock that has been issued. As of March 31, 2026, we had outstanding an aggregate of $75 million of subordinated notes and we did not have any outstanding preferred stock or trust preferred securities. We could incur future debt obligations or issue preferred stock in the future to raise additional capital. In such event, holders of our common stock will not be entitled to receive any payment or other distribution of assets upon the liquidation, dissolution or winding up of the Company until after all of our obligations to the debt holders are satisfied and holders of subordinated debt and senior equity securities, including preferred shares, if any, have received any payment or distribution due to them. In addition, we are required to pay interest on the subordinated notes and dividends on any trust preferred securities and preferred stock before we are able to pay any dividends on our common stock. Since any decision to issue debt securities

S-16

or incur other borrowings in the future will depend on market conditions and other factors beyond our control, the amount, timing, nature or success of our future capital raising efforts is uncertain. Thus, holders of our common stock bear the risk that our future issuances of debt securities or our incurrence of other borrowings will negatively affect the market price of our common stock.

Our management will have broad discretion in allocating the net proceeds of the offering. Our failure to effectively utilize such net proceeds may have an adverse effect on our financial performance and the value of our common stock.

We intend to use the net proceeds from this offering for general corporate purposes and to support our continued growth, including through investments in the Bank to pursue growth opportunities, and for working capital. However, we are not required to apply any portion of the net proceeds of this offering for any particular purpose and our management could use the proceeds for purposes other than those contemplated at the time of this offering. Accordingly, our management will have broad discretion in the application of the net proceeds from this offering, and you will be relying on the judgment of our management regarding the application of these proceeds. You will not have the opportunity, as part of your investment decision, to assess whether we are using the proceeds appropriately. Our management might not apply our net proceeds in ways that ultimately increase the value of your investment. If we do not invest or apply the net proceeds from this offering in ways that enhance shareholder value, we may fail to achieve expected financial results, which could cause the market price of our stock to decline.

California law and the provisions of our articles of incorporation and amended and restated bylaws, or our bylaws, may have an anti-takeover effect, and there are substantial regulatory limitations on changes of control of bank holding companies.

California corporate law and provisions of our articles of incorporation and our bylaws could make it more difficult for a third party to acquire us, even if doing so would be perceived to be beneficial by our shareholders.

Furthermore, prior approval of the Federal Reserve and the DFPI is generally required for any person to acquire control of the Company. Under federal and state laws, a person may be presumed to acquire control of the Company if the person acquires 10% or more of our outstanding common stock. In addition, Federal Reserve approval is also generally required for a bank holding company to acquire 5% or more of our outstanding common stock. Accordingly, prospective investors must comply with these requirements, if applicable, in connection with any purchase of shares of our common stock. Collectively, provisions of our articles of incorporation and bylaws and other statutory and regulatory provisions may delay, prevent, or deter a merger, acquisition, tender offer, proxy contest, or other transaction that might otherwise result in our shareholders receiving a premium over the market price for their common stock. Moreover, the combination of these provisions effectively inhibits certain business combinations, which, in turn, could adversely affect the market price of our common stock.

An investment in our common stock is not an insured deposit and is not guaranteed by the FDIC, so you could lose some or all of your investment.

An investment in our common stock is not a bank deposit and, therefore, is not insured against loss or guaranteed by the FDIC, any other deposit insurance fund or by any other public or private entity. Investment in our common stock is inherently risky for the reasons described herein, and is subject to the same market forces that affect the price of common stock in any company. As a result, if you acquire our common stock, you could lose some or all of your investment.

Our preliminary financial information is based on information available as of the date of this prospectus supplement and may be subject to change.

All financial data in this prospectus supplement for the three and six months ended June 30, 2026 is preliminary. These preliminary results are not a comprehensive statement of our financial position for the three and six months ended June 30, 2026 and are based on information available as of the date of this prospectus supplement. During the course of the preparation of our quarterly financial statements and related notes,

S-17

we may identify items that would require the Company to make adjustments to the preliminary financial information presented in this prospectus supplement. The actual amounts that we report will be subject to any final adjustments that may be made prior to the time our financial results for the three and six months ended June 30, 2026 are finalized and filed with the SEC in our Quarterly Report on Form 10-Q for the quarter ended June 30, 2026, and may differ materially from the preliminary financial information included in this prospectus supplement.

Risks Relating to Our Business and our Industry and Regulation

For risks associated with our business and industry, see the section entitled “Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2025, as well as in each subsequently filed Quarterly Report on Form 10-Q, and other filings we may make with the SEC, which are incorporated into this prospectus supplement by reference, as the same may be updated from time to time prior to the completion of this offering by our future filings under the Exchange Act.

S-18

USE OF PROCEEDS

We estimate that the net proceeds to us from this offering will be approximately $ million, or approximately $ million if the underwriters exercise in full their option to purchase additional shares, in each case, after deducting underwriting discounts and commissions and the estimated offering expenses payable by us.

Our board of directors and management will have broad discretion in the application of the net proceeds from this offering, and investors will be relying on the judgment of our board of directors and management with regard to the use of these net proceeds. Pending the use of the net proceeds from this offering as described above, we may invest the net proceeds in short-term liquid instruments.

S-19

CAPITALIZATION

The following table sets forth our capitalization as of March 31, 2026:

on an actual basis; and

on an as adjusted basis to reflect the sale of shares of our common stock offered by us at the public offering price of $ per share in this offering, after deducting the underwriting discount and our estimated offering expenses (assuming the underwriters’ option to purchase additional shares from us is not exercised).

This table should be read in conjunction with, and is qualified in its entirety by reference to, the information appearing under “Use of Proceeds” included elsewhere in this prospectus supplement, our historical financial statements and related notes incorporated by reference into this prospectus supplement.

	As of March 31, 2026
*(Dollars in thousands)*	Actual			As Adjusted
Borrowings:
Subordinated notes (due 2032)	$	74,077		$	74,077

Shareholders’ equity:
Preferred stock, no par value; 10,000,000 shares authorized; zero issued and outstanding		—			—
Common stock, no par value; 100,000,000 shares authorized; 21,376,153 shares issued and outstanding - actual and shares issued and outstanding - as adjusted		304,372
Retained earnings		164,262
Accumulated other comprehensive loss, net of taxes		(10,115	)
Total shareholders’ equity		458,519		$

Total capitalization	$	532,596		$
Capital ratios:
Total capital (to risk-weighted assets)		13.17	%			%
Tier 1 capital (to risk-weighted assets)		10.45	%			%
Common equity Tier 1 capital (to risk-weighted assets)		10.45	%			%
Tier 1 leverage		9.56	%			%
Total shareholders’ equity to total assets		9.11	%			%

S-20

MATERIAL U.S. FEDERAL INCOME TAX CONSIDERATIONS TO NON-U.S. HOLDERS

The following discussion is a summary of the material U.S. federal income tax consequences of the purchase, ownership and disposition of our common stock by Non-U.S. Holders (as defined below) that acquire our common stock in this offering and hold it as a capital asset within the meaning of Section 1221 of the Internal Revenue Code of 1986, as amended, or the Code (generally, property held for investment). This discussion does not purport to be a complete analysis of all potential tax effects. All prospective holders of our common stock should consult their tax advisors with respect to the U.S. federal, state, local, and non-U.S. tax consequences of the purchase, ownership, and disposition of our common stock. The effects of other U.S. federal tax laws, such as estate and gift tax laws, and any applicable state, local or non-U.S. tax laws are not discussed. This discussion is based on the Code, Treasury Regulations promulgated thereunder, judicial decisions, and published rulings and administrative pronouncements of the Internal Revenue Service, or the IRS, in each case in effect as of the date of this prospectus supplement. These authorities may change or be subject to differing interpretations at any time. Any such change or differing interpretation may be applied retroactively in a manner that could adversely affect a Non-U.S. Holder of our common stock. We have not sought and will not seek any rulings from the IRS regarding the statements made and the conclusions reached in the discussion below. There can be no assurance the IRS or a court will agree with our position discussed below regarding the U.S. federal income tax consequences of the purchase, ownership and disposition of our common stock. We cannot assure you that a change in law will not significantly alter the tax considerations described in this discussion.

This discussion does not address all U.S. federal income tax consequences that may be relevant to a Non-U.S. Holder’s particular circumstances, including the alternative minimum tax, estate or gift tax consequences, and the impact of the Medicare contribution tax on net investment income. In addition, it does not address consequences relevant to Non-U.S. Holders subject to special rules, including, without limitation:

U.S. expatriates and former citizens or long-term residents of the United States;

persons who have elected to mark securities to market or who hold our common stock as part of a hedge, straddle or other risk reduction strategy or as part of a conversion transaction or other integrated investment;

banks, insurance companies, mutual funds and other financial institutions;

corporations that accumulate earnings to avoid U.S. federal income tax;

“qualified foreign pension funds,” or entities wholly owned by a “qualified foreign pension fund”;

brokers, dealers or traders in securities;

tax-exempt organizations, pension plans, tax-qualified retirement plans, or governmental organizations;

persons having a functional currency other than the U.S. dollar; and

persons deemed to sell our common stock under the constructive sale provisions of the Code.

In addition, this discussion does not address the tax treatment of partnerships or persons that hold our common stock through such partnerships. If an entity or arrangement treated as a partnership for U.S. federal income tax purposes holds our common stock, the tax treatment of a partner in the partnership will generally depend on the status of the partner and the activities of the partnership. Accordingly, partnerships (and other entities or arrangements so treated for U.S. federal income tax purposes) holding our common stock and the partners in such partnerships should consult their tax advisors regarding the U.S. federal income tax consequences to them.

THIS DISCUSSION IS FOR INFORMATION PURPOSES ONLY AND IS NOT TAX ADVICE. INVESTORS SHOULD CONSULT THEIR TAX ADVISORS WITH RESPECT TO THE APPLICATION OF THE U.S. FEDERAL INCOME TAX LAWS TO THEIR PARTICULAR SITUATIONS AS WELL AS ANY TAX CONSEQUENCES OF THE PURCHASE, OWNERSHIP AND DISPOSITION OF OUR COMMON STOCK ARISING UNDER THE U.S. FEDERAL ESTATE OR GIFT TAX LAWS OR UNDER THE LAWS OF ANY STATE, LOCAL OR NON-U.S. TAXING JURISDICTION OR UNDER ANY APPLICABLE INCOME TAX TREATY.

S-21

Definition of a Non-U.S. Holder

For purposes of this discussion, a “Non-U.S. Holder” is any beneficial owner of our common stock that is, or is treated as, for U.S. federal income tax purposes:

a non-resident alien;

a foreign corporation (or any other foreign entity treated as a corporation for U.S. federal income tax purposes);

an estate, the income of which is not subject to U.S. federal income taxation regardless of its source; or

a trust that does not have in effect a valid election under the U.S. Treasury Regulations, to be treated as a United States person and either (i) no court within the United States is able to exercise primary supervision over the trust’s administration or (ii) no “United States person” (within the meaning of Section 7701(a)(30) of the Code) has the authority to control all substantial decisions of that trust.

Distributions on Common Stock

Distributions of cash or property on our common stock will generally constitute dividends for U.S. federal income tax purposes to the extent of our current or accumulated earnings and profits, as determined under U.S. federal income tax principles. Amounts not treated as dividends for U.S. federal income tax purposes will first constitute a tax-free return of capital to the extent of a Non-U.S. Holder’s adjusted tax basis in its common stock and thereafter capital gain, which is subject to the tax treatment described below in the section entitled “—Sale or Other Taxable Disposition”.

Subject to the discussion below in the sections entitled “–Information Reporting and Backup Withholding” and “–FATCA Withholding” and the discussion below on effectively connected income, dividends paid to a Non-U.S. Holder will generally be subject to U.S. federal withholding tax at a rate of 30% of the gross amount of the dividends or such lower rate specified by an applicable income tax treaty. To receive a reduced withholding rate, a Non-U.S. Holder must furnish a valid IRS Form W-8BEN or W-8BEN-E, as applicable, (or other applicable documentation) certifying qualification for the lower treaty rate. A Non-U.S. Holder that holds our common stock through a financial institution or other agent will be required to provide appropriate documentation to the financial institution or other agent, which then will be required to provide certification to us or our paying agent either directly or through other intermediaries. A Non-U.S. Holder that does not timely furnish the required documentation, but that qualifies for a reduced income tax treaty rate, may obtain a refund of any excess amounts withheld by timely filing an appropriate claim for refund with the IRS.

If dividends paid to a Non-U.S. Holder are effectively connected with the Non-U.S. Holder’s conduct of a trade or business within the United States (and, as provided by an applicable income tax treaty, attributable to a permanent establishment or fixed base maintained by the Non-U.S. Holder in the United States), the Non-U.S. Holder will be exempt from the U.S. federal withholding tax described above. To claim the exemption, the Non-U.S. Holder must furnish to the applicable withholding agent a valid IRS Form W-8ECI certifying that the dividends are effectively connected with the Non-U.S. Holder’s conduct of a trade or business within the United States.

Any such effectively connected dividends will be subject to U.S. federal income tax on a net income basis at the regular rates that also apply to U.S. persons. A Non-U.S. Holder that is a corporation also may be subject to a branch profits tax at a rate of 30% (or such lower rate specified by an applicable income tax treaty) on such effectively connected dividends, as adjusted for certain items. Non-U.S. Holders should consult their tax advisors regarding any applicable tax treaties and their entitlement to benefits thereunder.

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Sale or Other Taxable Disposition

Subject to the discussion below under “–Information Reporting and Backup Withholding” and “–FATCA Withholding,” a Non-U.S. Holder generally will not be subject to U.S. federal income tax or withholding tax on any gain realized upon the sale or other taxable disposition of our common stock (including a redemption, but only if the redemption would be treated as a sale or exchange rather than a distribution for U.S. federal income tax purposes) unless:

the gain is “effectively connected” with the Non-U.S. Holder’s conduct of a trade or business within the United States (and, if required by an applicable income tax treaty, attributable to a permanent establishment or fixed base maintained by the Non-U.S. Holder in the United States), in which case the Non-U.S. Holder generally will be subject to U.S. federal income tax on a net income basis with respect to such gain in the same manner as if such holder were a resident of the United States and, if the Non-U.S. Holder is a corporation for U.S. federal income tax purposes, may, under certain circumstances, be subject to an additional “branch profits tax” at a 30% rate (or at a lower rate under an applicable income tax treaty) on its “effectively connected” gains;

the Non-U.S. Holder is a nonresident alien individual present in the United States for 183 days or more during the taxable year of the disposition and certain other requirements are met, in which case the Non-U.S. Holder generally will be subject to U.S. federal income tax at a 30% rate (or at a lower rate under an applicable income tax treaty) on the gain derived from the sale, which gain may be offset by U.S.-source capital losses for the year; or

we are or have been a United States real property holding corporation (“USRPHC” as described below) at any time within the shorter of the five-year period preceding the disposition or the Non-U.S. Holder’s holding period for our common stock (the “relevant period”) and the Non-U.S. Holder (i) disposes of our common stock during a calendar year when our common stock is no longer regularly traded on an established securities market or (ii) owned (actually or constructively) more than 5% of our common stock at any time during the relevant period, in which case such a Non-U.S. Holder will be subject to tax on the gain on the disposition of shares generally as if the gain were effectively connected with the conduct of a trade or business in the United States, except that the “branch profits tax” will not apply.

We believe we currently are not, and do not anticipate becoming, a USRPHC. Generally, a corporation is a USRPHC only if the fair market value of its United States real property interests (as defined in the Code) equals or exceeds 50% of the sum of the fair market value of its worldwide real property interests and its other assets used or held for use in a trade or business.

Information Reporting and Backup Withholding

Payments of dividends on our common stock and the payment of the proceeds from the sale of our common stock effected at a U.S. office of a broker generally will not be subject to backup withholding and the payment of proceeds from the sale of our common stock effected at a U.S. office of a broker will generally not be subject to information reporting, provided the applicable withholding agent does not have actual knowledge or reason to know the Non-U.S. Holder is a United States person and the Non-U.S. Holder either certifies its non-U.S. status, such as by furnishing a valid IRS Form W-8BEN or W-8BEN-E, as applicable, or other documentation upon which it may rely to treat the payments as made to a non-U.S. person in accordance with Treasury Regulations or otherwise establishes an exemption.

However, we are required to file information returns with the IRS in connection with any distribution on our common stock paid to a Non-U.S. Holder, regardless of whether any tax was actually withheld. Copies of information returns that are filed with the IRS may also be made available under the provisions of an applicable treaty or agreement to the tax authorities of the country in which the Non-U.S. Holder resides or is established.

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Payment of the proceeds from the sale of our common stock effected at a foreign office of a broker generally will not be subject to information reporting or backup withholding. However, a sale of our common stock by a Non-U.S. Holder that is effected at a foreign office of a broker will be subject to information reporting and backup withholding if (i) the proceeds are transferred to an account maintained by the Non-U.S. Holder in the United States, (ii) the payment of proceeds or the confirmation of the sale is mailed to the Non-U.S. Holder at a U.S. address or (iii) the sale has some other specified connection with the United States as provided in the Treasury Regulations, unless, in each case, the broker does not have actual knowledge or reason to know that the holder is a United States person and the documentation requirements described above are met or the Non-U.S. Holder otherwise establishes an exemption.

In addition, a sale of our common stock will be subject to information reporting if it is effected at a foreign office of a broker that is (i) a United States person, (ii) a “controlled foreign corporation” for U.S. federal income tax purposes, (iii) a foreign person 50% or more of whose gross income is effectively connected with the conduct of a U.S. trade or business for a specified three-year period or (iv) a foreign partnership, if at any time during its tax year (a) one or more of its partners are “U.S. persons,” as defined in the Treasury Regulations, who in the aggregate hold more than 50% of the income or capital interest in the partnership or (b) such foreign partnership is engaged in the conduct of a trade or business in the United States, in each case unless the broker does not have actual knowledge or reason to know that the holder is a United States person and the documentation requirements described above are met or an exemption is otherwise established. Backup withholding will apply if the sale is subject to information reporting and the broker has actual knowledge that the holder is a United States person. Non-U.S. Holders should consult their tax advisors regarding the application of the information reporting and backup withholding rules to them.

Backup withholding is not an additional tax. Any amounts withheld under the backup withholding rules may be allowed as a refund or a credit against a Non-U.S. Holder’s U.S. federal income tax liability, provided the required information is timely furnished to the IRS.

FATCA Withholding

Sections 1471 through 1474 of the Code and the Treasury Regulations issued thereunder (commonly referred to as the Foreign Account Tax Compliance Act (“FATCA”)) impose a 30% withholding tax on dividends paid on our shares to, and (subject to the proposed Treasury Regulations discussed below) the gross proceeds derived from the sale or other disposition of our shares by, a foreign entity if the foreign entity is:

a “foreign financial institution” (as defined under FATCA) that does not furnish proper documentation, typically on IRS Form W-8BEN-E, evidencing either (i) an exemption from FATCA withholding or (ii) its compliance (or deemed compliance) with specified due diligence, reporting, withholding and certification obligations under FATCA or (iii) residence in a jurisdiction that has entered into an intergovernmental agreement with the United States relating to FATCA and compliance with the diligence and reporting requirements of the intergovernmental agreement and local implementing rules; or

a “non-financial foreign entity” (as defined under FATCA) that does not provide sufficient documentation, typically on IRS Form W-8BEN-E, evidencing either (i) an exemption from FATCA or (ii) adequate information regarding substantial United States beneficial owners of such entity (if any).

Withholding under FATCA generally applies to payments of dividends on our shares and to payments of gross proceeds from a sale or other disposition of our shares. Withholding agents may, however, rely on proposed U.S. Treasury Regulations that would no longer require FATCA withholding on payments of gross proceeds. A withholding agent such as a broker, and not the Company, will determine whether or not to implement gross proceeds FATCA withholding.

If a dividend payment is subject to withholding both under FATCA and the withholding tax rules discussed above in the section entitled “—Distributions on Common Stock,” the withholding under FATCA may be credited against, and therefore reduce, such other withholding tax. Holders of shares should consult their own tax advisors regarding these requirements and whether they may be relevant to their ownership and disposition of the shares.

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Under certain circumstances, a Non-U.S. Holder will be eligible for refunds or credits of withholding taxes imposed under FATCA by filing a United States federal income tax return. Prospective investors should consult their tax advisors regarding the effect of FATCA on their ownership and disposition of our shares.

EACH PROSPECTIVE INVESTOR SHOULD CONSULT ITS TAX ADVISOR REGARDING THE PARTICULAR U.S. FEDERAL, STATE, LOCAL, AND NON-U.S. TAX CONSEQUENCES OF PURCHASING, HOLDING, AND DISPOSING OF OUR COMMON STOCK, INCLUDING THE CONSEQUENCES OF ANY PROPOSED CHANGE IN APPLICABLE LAWS.

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UNDERWRITING

We are offering the shares of our common stock described in this prospectus supplement in an underwritten offering in which we and Keefe, Bruyette & Woods, Inc., as representative for the underwriters named below, are entering into an underwriting agreement with respect to the shares of our common stock being offered hereby. Subject to certain conditions, we will agree to sell, and each underwriter will severally and not jointly agree to purchase, the number of shares of our common stock indicated in the following table:

		Number of Shares
Keefe, Bruyette & Woods, Inc.
Stephens Inc.
D.A. Davidson & Co.
Raymond James & Associates, Inc.
Brean Capital, LLC
Total

The underwriters are offering the shares of our common stock subject to a number of conditions, including receipt and acceptance of our common stock by the underwriters. The obligations of the underwriters to pay for and accept delivery of the shares offered by this prospectus supplement are subject to these conditions. The underwriting agreement between us and the underwriters provides that if any underwriter defaults, the purchase commitments of the non-defaulting underwriters may be increased or this offering may be terminated.

In connection with this offering, the underwriters or securities dealers may distribute offering documents to investors electronically. See the section entitled “—Electronic Distribution.”

Underwriting Discount

Shares of our common stock sold by the underwriters to the public will be offered at the public offering price set forth on the cover of this prospectus supplement. Any shares of our common stock sold by the underwriters to securities dealers may be sold at a discount of up to $ per share from the public offering price. Any of these securities dealers may resell any shares of our common stock purchased from the underwriters to other brokers or dealers at a discount of up to $ per share from the public offering price. If all of the shares of our common stock are not sold at the public offering price, the representative may change the offering price and the other selling terms. Sales of shares of our common stock made outside of the United States may be made by affiliates of the underwriters. The underwriters reserve the right to reject an order for the purchase of shares, in whole or in part.

The underwriting fee is equal to the public offering price per share of common stock less the amount paid by the underwriters to us per share of common stock. The underwriting fee is $ per share. The following table shows the per share and total underwriting discounts to be paid to the underwriters assuming both no exercise and full exercise of the underwriters’ option to purchase additional shares.

	Full Exercise of option to purchase additional shares	No Exercise of option to purchase additional shares
Per share	$	$
Total	$	$

We estimate the expenses of this offering, not including the underwriting discount, to be approximately $ million, and such expenses are payable by us. We also have agreed to reimburse the underwriters for their expenses incurred in connection with the offering in an amount up to $250,000.

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Option to Purchase Additional Shares

We have granted the underwriters an option to purchase up to additional shares of our common stock, at the public offering price set forth on the cover page of this prospectus supplement, less the underwriting discount. The underwriters may exercise this option, in whole or in part, from time to time for a period of 30 days from the date of this prospectus supplement. If the underwriters exercise this option, each underwriter will be obligated, subject to the conditions in the underwriting agreement, to purchase a number of additional shares of our common stock proportionate to the number of shares reflected next to such underwriter’s name in the table above relative to the total number of shares reflected in such table.

Lock-Up Agreements

We, our executive officers and directors have agreed with the underwriters not to, without the prior written approval of the representative and subject to certain exceptions:

offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant for the sale of, or otherwise dispose of or transfer any shares of our common stock or any securities convertible into or exchangeable or exercisable for our common stock, whether now owned or hereafter acquired or with respect to which such person has or hereafter acquires the power of disposition, or exercise any right with respect to the registration thereof, or file or cause to be filed any registration statement under the Securities Act, with respect to any of the foregoing;

enter into any swap, hedge, or any other agreement or any transaction that transfers, in whole or in part, directly or indirectly, the economic consequence of ownership of the shares of our common stock or such other securities, whether any such swap or transaction is to be settled by delivery of shares of our common stock or other securities, in cash or otherwise; or

publicly disclose the intention to make any such offer, pledge, sale or disposition, or to enter into any such swap, hedge, transaction or other arrangement.

These restrictions are subject to customary exceptions and will be in effect for a period of 90 days after the date of this prospectus supplement. At any time and without public notice, the representative may, in their sole discretion, waive or release all or some of the securities from these lock-up agreements.

These restrictions also apply to securities convertible into or exchangeable or exercisable for or repayable with our common stock to the same extent as they apply to our common stock. They also apply to common stock owned now or later acquired by the person executing the agreement or for which the person executing the agreement later acquires the power of disposition.

Exchange Listing

Our common stock is listed on the Nasdaq Global Select Market under the symbol “FSBC.”

Indemnification and Contribution

We have agreed to indemnify the underwriters and their affiliates, selling agents, and controlling persons against certain liabilities, including under the Securities Act. If we are unable to provide this indemnification, we will contribute to the payments the underwriters and their affiliates, selling agents, and controlling persons may be required to make in respect of those liabilities.

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Price Stabilization, Short Positions, and Penalty Bids

To facilitate this offering and in accordance with Regulation M under the Exchange Act, the underwriters may engage in transactions that stabilize, maintain, or otherwise affect the price of our common stock, including:

stabilizing transactions;

short sales; and

purchase to cover positions created by short sales.

Stabilizing transactions consist of bids or purchases made for the purpose of preventing or retarding a decline in the market price of our common stock while this offering is in progress. These transactions may also include making short sales of our common stock, which involves the sale by the underwriters of a greater number of shares of common stock than they are required to purchase in this offering. Short sales may be “covered short sales,” which are short positions in an amount not greater than the underwriters’ purchase option referred to above, or may be “naked short sales,” which are short positions in excess of that amount.

The underwriters may close out any covered short position either by exercising their purchase option, in whole or in part, or by purchasing shares in the open market. In making this determination, the underwriters will consider, among other things, the price of shares available for purchase in the open market compared to the price at which they may purchase shares through the purchase option described above. The underwriters must close out any naked short position by purchasing shares in the open market. A naked short position is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of our common stock in the open market that could adversely affect investors who purchased in this offering.

As an additional means of facilitating our public offering, the underwriters may bid for, and purchase, shares of our common stock in the open market. The underwriting syndicate also may reclaim selling concessions allowed to an underwriter or a dealer for distributing shares of our common stock in this offering, if the syndicate repurchases previously distributed shares of our common stock to cover syndicate short positions or to stabilize the price of our common stock.

As a result of these activities, the price of our common stock may be higher than the price that otherwise might exist in the open market. If these activities are commenced, they may be discontinued by the underwriters at any time without notice. The underwriters may carry out these transactions on the Nasdaq Global Select Market, in the over-the-counter market or otherwise.

Electronic Distribution

A prospectus supplement in electronic format may be made available by e-mail or on the websites or through online services maintained by one or more of the underwriters or their affiliates. In those cases, prospective investors may view offering terms online and may be allowed to place orders online. The underwriters may agree with us to allocate a specific number of shares for sale to online brokerage account holders. Any such allocation for online distributions will be made by the underwriters on the same basis as other allocations. Other than the prospectus supplement in electronic format, the information on the underwriters’ websites and any information contained on any other website maintained by any of the underwriters is not part of this prospectus supplement, has not been approved and/or endorsed by the underwriters or us, and should not be relied upon by investors.

S-28

Affiliations

The underwriters and their respective affiliates are full service financial institutions engaged in various activities, which may include securities trading, commercial and investment banking, financial advisory, investment management, investment advisory, investment research, principal investment, hedging, financing, loan referrals, valuation, and brokerage activities. From time to time, the underwriters and/or their respective affiliates have directly and indirectly engaged, and may in the future engage, in various financial advisory, investment banking loan referrals, and commercial banking services with us and our affiliates, for which they received or paid, or may receive or pay, customary compensation, fees, and expense reimbursement. In the ordinary course of their various business activities, the underwriters and their respective affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers, and those investment and securities activities may involve securities and/or instruments of ours. The underwriters and their respective affiliates may also make investment recommendations and/or publish or express independent research views in respect of those securities or instruments and may at any time hold, or recommend to clients that they acquire, long and/or short positions in those securities and instruments.

Selling Restrictions

Canada

The shares may be sold only to purchasers purchasing, or deemed to be purchasing, as principal that are accredited investors, as defined in National Instrument 45-106 Prospectus Exemptions or subsection 73.3(1) of the Securities Act (Ontario), and are permitted clients, as defined in National Instrument 31-103 Registration Requirements, Exemptions and Ongoing Registrant Obligations. Any resale of the shares must be made in accordance with an exemption from, or in a transaction not subject to, the prospectus requirements of applicable securities laws.

Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if this prospectus supplement (including any amendment thereto) contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser’s province or territory. The purchaser should refer to any applicable provisions of the securities legislation of the purchaser’s province or territory for particulars of these rights or consult with a legal advisor.

Pursuant to section 3A.3 of National Instrument 33-105 Underwriting Conflicts (NI 33-105), the underwriters are not required to comply with the disclosure requirements of NI 33-105 regarding underwriter conflicts of interest in connection with this offering.

European Economic Area

In relation to each Member State of the European Economic Area (each a “Relevant State”), no shares have been offered or will be offered pursuant to the offering to the public in that Relevant State prior to the publication of a prospectus in relation to the Shares which has been approved by the competent authority in that Relevant State or, where appropriate, approved in another Relevant State and notified to the competent authority in that Relevant State, all in accordance with the Prospectus Regulation, except that the Shares may be offered to the public in that Relevant State at any time:

(a)

to any qualified investor as defined under Article 2 of the Prospectus Regulation;

(b)

to fewer than 150 natural or legal persons (other than qualified investors as defined under Article 2 of the Prospectus Regulation), subject to obtaining the prior consent of the underwriters for any such offer; or

(c)

in any other circumstances falling within Article 1(4) of the Prospectus Regulation,

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provided that no such offer of the Shares shall require the Company or any underwriter to publish a prospectus pursuant to Article 3 of the Prospectus Regulation, supplement a prospectus pursuant to Article 23 of the Prospectus Regulation or publish an Annex IX document pursuant to Article 1(4) of the Prospectus Regulation.

For the purposes of this provision, the expression an “offer to the public” in relation to the Shares in any Relevant State means the communication in any form and by any means of sufficient information on the terms of the offer and any Shares to be offered so as to enable an investor to decide to purchase for any Shares, and the expression “Prospectus Regulation” means Regulation (EU) 2017/1129.

United Kingdom

No shares have been offered or will be offered pursuant to the offering to the public in the United Kingdom except that the Shares may be offered to the public in the United Kingdom at any time:

(a)

where the offer is conditional on the admission of the Shares to trading on the London Stock Exchange plc’s main market (in reliance on the exception in paragraph 6(a) of Schedule 1 of the POATR);

(b)

to any qualified investor as defined under paragraph 15 of Schedule 1 of the POATR;

(c)

to fewer than 150 persons (other than qualified investors as defined under paragraph 15 of Schedule 1 of the POATR), subject to obtaining the prior consent of the underwriters for any such offer; or

(d)

in any other circumstances falling within Part 1 of Schedule 1 of the POATR.

For the purposes of this provision, the expression an “offer to the public” in relation to the Shares in the United Kingdom means the communication to any person which presents sufficient information on: (a) the Shares to be offered; and (b) the terms on which they are to be offered, to enable an investor to decide to buy or subscribe for the Shares and the expressions “POATR” means the Public Offers and Admissions to Trading Regulations 2024.

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LEGAL MATTERS

The validity of the shares of common stock offered hereby and certain other legal matters in connection with the offering will be passed upon for us by Covington & Burling LLP, Washington, D.C. Latham & Watkins LLP, Los Angeles, California, will pass upon certain legal matters for the underwriters.

EXPERTS

The consolidated financial statements of Five Star Bancorp incorporated in this prospectus by reference from the Company’s Annual Report on Form 10-K for the year ended December 31, 2025, have been audited by Baker Tilly US, LLP, an independent registered public accounting firm, as stated in their report. Such consolidated financial statements are incorporated by reference in reliance upon the report of such firm given their authority as experts in accounting and auditing.

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PROSPECTUS

$300,000,000

Common Stock

Preferred Stock

Debt Securities

Depositary Shares

Warrants

Purchase Contracts

Purchase Units

Subscription Rights

Units

We may offer, issue and sell, from time to time up to $300,000,000, together or separately, in one or more offerings, the above-referenced securities. The securities we may offer may be convertible into or exchangeable for other securities. This prospectus describes some of the general terms that may apply to these securities and the general manner in which they may be offered. Each time we offer any securities pursuant to this prospectus, we will provide you with a prospectus supplement that will describe the specific amounts, prices and terms of the securities being offered and the specific manner in which they may be offered. You should read this prospectus, the information incorporated by reference in this prospectus, the accompanying prospectus supplement, including any information incorporated by reference therein, and any applicable free writing prospectus carefully before you invest in the securities described in the applicable prospectus supplement.

Our common stock is listed on the Nasdaq Global Select Market (“Nasdaq”) and trades under the ticker symbol “FSBC.”

We may offer and sell these securities to or through one or more underwriters, dealers and agents, directly to purchasers or through a combination of these methods, on a continuous or delayed basis from time to time. See “Plan of Distribution.” The names of any underwriters, dealers or agents involved in the distribution of our securities, their compensation and any option they hold to acquire additional securities will be described in the applicable prospectus supplement. Net proceeds from the sale of securities will be set forth in the applicable prospectus supplement.

Investing in our securities involves certain risks. Before buying our securities, you should carefully consider the risks described under the caption “Risk Factors” beginning on page 2 of this prospectus, any similar section contained in the applicable prospectus supplement and in any free writing prospectus we have authorized for use in connection with a specific offering, and under similar headings in the documents incorporated by reference in this prospectus, and in the documents included or incorporated by reference into this prospectus and the accompanying prospectus supplement, including any information incorporated by reference therein.

These securities are not deposits, savings accounts or other obligations of any bank or savings association and are not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency and are subject to investment risks, including the possible loss of the entire amount you invest.

None of the U.S. Securities and Exchange Commission, any state securities commission, the Federal Deposit Insurance Corporation, the Board of Governors of the Federal Reserve System or any other regulatory body has approved or disapproved of these securities or determined if this prospectus is accurate or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is February 9, 2026.

TABLE OF CONTENTS

	Page

ABOUT THIS PROSPECTUS	ii
WHERE YOU CAN FIND MORE INFORMATION	iii
FORWARD-LOOKING STATEMENTS	iv
THE COMPANY	1
RISK FACTORS	2
USE OF PROCEEDS	3
DESCRIPTION OF SECURITIES WE MAY OFFER	4
DESCRIPTION OF COMMON STOCK	5
DESCRIPTION OF PREFERRED STOCK	10
DESCRIPTION OF DEBT SECURITIES	13
DESCRIPTION OF DEPOSITARY SHARES	26
DESCRIPTION OF WARRANTS	29
DESCRIPTION OF PURCHASE CONTRACTS AND PURCHASE UNITS	31
DESCRIPTION OF SUBSCRIPTION RIGHTS	32
DESCRIPTION OF UNITS	33
PLAN OF DISTRIBUTION	34
LEGAL MATTERS	37
EXPERTS	37

ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement on Form S-3 that we filed with the U.S. Securities and Exchange Commission (“SEC”), using a “shelf” registration process. Under this shelf registration statement, we may offer and sell from time to time, separately or together, any combination of our common stock, preferred stock, debt securities, depositary shares, warrants, purchase contracts, purchase units, subscription rights and units in one or more offerings at an aggregate offering price of up to $300,000,000. The preferred stock, debt securities, warrants, purchase contracts, purchase units, subscription rights and units may be convertible into, or exercisable or exchangeable for, our common or preferred stock or other securities issued by us, or debt or equity securities issued by one or more other entities.

This prospectus provides you with a general description of the securities we may offer. Each time we offer and sell securities, we will provide a prospectus supplement that will contain specific information about the terms of that offering. The prospectus supplement may also add, update or change information contained in this prospectus. You should read this prospectus and the applicable prospectus supplement together with the additional information described under the heading “Where You Can Find More Information.” We may also prepare free writing prospectuses that describe particular securities. Any free writing prospectus should also be read in connection with this prospectus and any prospectus supplement referred to therein. For purposes of this prospectus, any reference to an applicable prospectus supplement may also refer to a free writing prospectus, unless the context otherwise requires. Unless otherwise indicated or the context otherwise requires, all references in this prospectus to “Five Star,” “we,” “our,” “us,” “our company” and “the Company” refer to Five Star Bancorp, a California corporation and the bank holding company for Five Star Bank, our principal subsidiary and a California state-chartered bank.

The registration statement of which this prospectus forms a part, including the exhibits to the registration statement, contains additional information about us and the securities offered under this prospectus. The registration statement can be obtained from the SEC’s website, www.sec.gov. Copies of information filed by us with the SEC are also available on the “Investor Relations” page of our website at https://investors.fivestarbank.com/. The reference to our website is not intended to be an active link and the information on, or that can be accessed through, our website is not, and you must not consider the information to be, a part of this prospectus or any other filings we make with the SEC.

We have not authorized anyone to provide you with information in addition to or different from that contained or incorporated by reference in this prospectus or any applicable prospectus supplement or free writing prospectus prepared by us or on our behalf. We take no responsibility for, and can provide no assurance as to the reliability of, any information that others may provide. We are not making an offer to sell or soliciting an offer to buy our securities under any circumstances where the offer or solicitation is not permitted. You should not assume that the information in this prospectus, any applicable prospectus supplement or any free writing prospectus that we have prepared is accurate as of any date other than the date of those documents, and that any information in documents that we have incorporated by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus or any prospectus supplement or any sale of a security. Our business, financial condition, results of operations and prospects may have changed since those dates.

The distribution of this prospectus and any applicable prospectus supplement and the offering of the securities in certain jurisdictions may be restricted by law. Persons who obtain this prospectus and any applicable prospectus supplement should inform themselves about, and observe, any such restrictions. This prospectus and any applicable prospectus supplement do not constitute, and may not be used in connection with, an offer or solicitation by anyone in any jurisdiction in which such offer or solicitation is not permitted or in which the person making such offer or solicitation is not qualified to do so or to any person to whom it is unlawful to make such offer or solicitation.

WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings are available to the public on the SEC’s website at www.sec.gov.

The SEC allows us to “incorporate by reference” into this prospectus the information in documents we file with the SEC, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be a part of this prospectus and should be read with the same care. When we update the information contained in documents that have been incorporated by reference by making future filings with the SEC, the information incorporated by reference into this prospectus is considered to be automatically updated and superseded. In other words, in all cases, if you are considering whether to rely on information contained in this prospectus or information incorporated by reference into this prospectus, you should rely on the information contained in the document that was filed later. We incorporate by reference (other than any information furnished to, rather than filed with, the SEC, unless expressly stated otherwise therein) the documents listed below (File No. 001-40379 unless otherwise stated), which are considered to be a part of this prospectus:

	·	our Annual Report on Form 10-K for the year ended December 31, 2024, filed with the SEC on February 28, 2025 (including the portions of our Definitive Proxy Statement on Schedule 14A, filed with the SEC on April 2, 2025, incorporated by reference therein);

	·	our Quarterly Reports on Form 10-Q for the quarter ended March 31, 2025, filed with the SEC on May 8, 2025, for the quarter ended June 30, 2025, filed with the SEC on August 7, 2025, and for the quarter ended September 30, 2025, filed with the SEC on November 6, 2025;
	·	our Current Reports on Form 8-K filed with the SEC on April 23, 2025; May 20, 2025; June 9, 2025; June 25, 2025; and November 5, 2025; and

the description of our common stock contained in our Registration Statement on Form S-1 (File No. 333-255143), which was incorporated by reference into our Registration Statement on Form 8-A filed with the SEC pursuant to Section 12(b) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), on May 3, 2021, including any amendment or report filed with the SEC for purposes of updating such description.

All reports and other documents we subsequently file with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act, including all such reports and other documents filed with the SEC after the date of the initial filing of the registration statement of which this prospectus forms a part and prior to the effectiveness of such registration statement, until our offering is completed will also be incorporated by reference into this prospectus and deemed to be part hereof (other than any information furnished to, rather than filed with, the SEC, unless expressly stated otherwise therein). The most recent information that we file with the SEC automatically updates and supersedes older information. The information contained in any such filing will be deemed to be a part of this prospectus commencing on the date on which the document is filed.

Any documents incorporated by reference into this prospectus are available without charge to you, upon written request on the Internet at https://investors.fivestarbank.com/ or upon written or oral request by contacting Heather Luck, Executive Vice President and Chief Financial Officer, at 3100 Zinfandel Drive, Suite 100, Rancho Cordova, California 95670, (916) 626-5000. The reference to our website is not intended to be an active link and the information on, or that can be accessed through, our website is not, and you must not consider the information to be, a part of this prospectus or any other filings we make with the SEC.

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FORWARD-LOOKING STATEMENTS

Certain statements included or incorporated by reference in this prospectus and each prospectus supplement may not be based on historical facts and are “forward-looking statements” within the meaning of Section 27A of the Securities Act, and Section 21E of the Exchange Act. These forward-looking statements reflect our current views with respect to, among other things, future events and our financial performance. Any statements about our management’s expectations, beliefs, plans, predictions, forecasts, objectives, assumptions or future events or performance are not historical facts and may be forward-looking. These statements are often, but not always, made through the use of words or phrases such as “anticipate,” “believes,” “can,” “could,” “may,” “predicts,” “potential,” “should,” “will,” “estimate,” “plans,” “projects,” “continuing,” “ongoing,” “expects,” “aim,” “intends” and similar words or phrases. All forward-looking statements, expressed or implied, included herewith are expressly qualified in their entirety by the cautionary statements contained or referred to herein. The inclusion of forward-looking information in this prospectus and each prospectus supplement, and the documents incorporated by reference herein and therein, should not be regarded as a representation by us or any other person that the future plans, estimates or expectations contemplated by us will be achieved. We have based these forward-looking statements largely on our current expectations and projections about future events and financial trends that we believe may affect our financial condition, results of operations, business strategy and financial needs. We caution that the forward-looking statements are based largely on our expectations and are subject to a number of known and unknown risks and uncertainties that are subject to change based on factors which are, in many instances, beyond our control. Factors that may affect our results are disclosed in “Risk Factors” beginning on page 2 of this prospectus, and in the documents incorporated by reference into this prospectus and included or incorporated by reference into, and in the section titled “Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2024. Some of the risks and uncertainties that may cause our actual results, performance or achievements to differ materially from those expressed include, but are not limited to, the following: