Five Star Bancorp美股招股说明书(2026-07-22版)

This preliminary prospectus supplement and the accompanying prospectus are part of an effective registration statement filedwith the Securities and Exchange Commission under the Securities Act of 1933, as amended, and the information in thispreliminary prospectus supplement is not complete and may be changed. This preliminary prospectus supplement and theaccompanying prospectus are not an offer to sell the securities described herein and are not soliciting an offer to buy thesesecurities 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 offeringshares 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 reportedclosing 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 aresult, 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 theinformation under the heading “Risk Factors” beginning on page S-14 of this prospectus supplement, on page 2 of theaccompanying prospectus and under the heading “Part I. Item 1A. Risk Factors” in our Annual Report onForm 10-Kfor theyear ended December 31, 2025, as well as in each subsequently filed Quarterly Report on Form 10-Q, and other filings we maymake with the U.S. Securities and Exchange Commission, or the SEC, which are incorporated herein by reference. PerShareTotal(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, topurchase up to an additionalshares 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 InsuranceCorporation, or the FDIC, the Board of Governors of the Federal Reserve System, or the Federal Reserve, the CaliforniaDepartment of Financial Protection and Innovation, or the DFPI, or any other regulatory authority has approved ordisapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful orcomplete. 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-banksubsidiary 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 ofcommon stock in this offering at a price equal to the public offering price. Because this indication of interest is not a bindingagreement or commitment to purchase, these persons could determine to purchase more, less or no shares in this offering or theunderwriters 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 prospectussupplement. The underwriters expect to deliver the shares of common stock in book-entry form only through the facilities of The TABLE OF CONTENTS Prospectus Supplement ABOUT THIS PROSPECTUS SUPPLEMENT AND THE ACCOMPANYING PROSPECTUSWHERE YOU CAN FIND MORE INFORMATIONINCORPORATION OF CERTAIN DOCUMENTS BY REFERENCESPECIAL CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTSPROSPECTUS SUPPLEMENT SUMMARYTHE OFFERINGRISK FACTORSUSE OF PROCEEDSCAPITALIZATIONMATERIAL U.S. FEDERAL INCOME TAX CONSIDERATIONS TO NON-U.S. HOLDERSUNDERWRITINGLEGAL MATTERSEXPERTS Prospectus ABOUT THIS PROSPECTUSWHERE YOU CAN FIND MORE INFORMATIONFORWARD-LOOKING STATEMENTSTHE COMPANYRISK FACTORSUSE OF PROCEEDSDESCRIPTION OF SECURITIES WE MAY OFFERDESCRIPTION OF COMMON STOCKDESCRIPTION OF PREFERRED STOCKDESCRIPTION OF DEBT SECURITIESDESCRIPTION OF DEPOSITARY SHARESDESCRIPTION OF WARRANTSDESCRIPTION OF PURCHASE CONTRACTS AND PURCHASE UNITSDESCRIPTION OF SUBSCRIPTION RIGHTSDESCRIPTION OF UNITSPLAN OF DISTRIBUTIONLEGAL MATTERSEXPERTS 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 ofthis offering of common stock, including the price, the number of