First Interstate BancSystem Inc-A美股招股说明书(2025-06-06版)

7.625% Fixed-to-Floating Rate Subordinated Notes due 2035 We are offering $125,000,000 aggregate principal amount of 7.625% Fixed-to-Floating Rate Subordinated Notes due 2035 (the“Notes”). The Notes will mature on June15, 2035. From and including the date of original issuance to, but excluding, June15, 2030or the date of earlier redemption, the Notes will bear interest at a rate of 7.625% per annum, payable semiannually in arrears onJune15 and December15 of each year, commencing on December15, 2025. From and including June15, 2030, to, but excluding,June15, 2035 or the date of earlier redemption, the Notes will bear interest at a floating rate per annum equal to a benchmark rate(which is expected to be Three-Month Term SOFR (as defined herein)) plus a spread of 398 basis points, payable quarterly in arrearson March15, June15, September15 and December15 of each year, commencing on September15, 2030. We may, at our option, redeem the Notes (i)in whole or in part beginning with the interest payment date of June15, 2030, and on anyinterest payment date thereafter or (ii)in whole but not in part upon the occurrence of a “Tax Event,” a “Tier 2 Capital Event” or FirstInterstate BancSystem, Inc. becoming required to register as an investment company pursuant to the Investment Company Act of1940, as amended (the “1940 Act”). The redemption price for any redemption is 100% of the principal amount of the Notes beingredeemed, plus accrued and unpaid interest thereon to, but excluding, the date of redemption. Any early redemption of the Notes willbe subject to the receipt of the approval of the Board of Governors of the Federal Reserve System to the extent then required underapplicable laws or regulations, including capital regulations. The Notes will rank junior to all of our existing and future senior indebtedness. In addition, the Notes will be effectively subordinatedto all of our secured indebtedness to the extent of the value of the assets securing such indebtedness. The Notes will be structurallysubordinated to all of the existing and future liabilities and obligations of our subsidiaries, including the deposit liabilities and claimsof other creditors of our bank subsidiary, First Interstate Bank. The Notes will rank equally in right of payment with our existing$100million aggregate principal amount of 5.25% Fixed-to-Floating Rate Subordinated Notes due 2030 (the “2020 SubordinatedNotes”), until such 2020 Subordinated Notes are redeemed by us on August15, 2025 as currently contemplated. See“Use ofProceeds” beginning on pageS-16. The Notes will be obligations of First Interstate BancSystem, Inc. only and will not be obligationsof, and will not be guaranteed by, any of our subsidiaries. The Notes will not be listed on any national securities exchange. Currently, there is no public market for the Notes. (1)Plus accrued interest, if any, from June10, 2025 to the date of delivery. (2)We have agreed to reimburse the underwriter for certain expenses in connection with this offering. See“Underwriting.”The underwriter expects to deliver the Notes in book-entry only form on or about June10, 2025. Investing in the Notes involves certain risks. Please read “Risk Factors” beginning on pageS-7of this prospectus supplement, on page5ofthe accompanying prospectus, beginning on page 15 of our Annual Report on Form 10-K for the year ended December31, 2024, andbeginning on page55 of our Quarterly Report on Form 10-Q for the quarter ended March31, 2025. None of the Securities and Exchange Commission, any state securities commission, the Board of Governors of the Federal Reserve System,the Federal Deposit Insurance Corporation (the “FDIC”), the Montana Division of Banking and Financial Institutions, or any otherregulatory body has approved or disapproved of the Notes or passed upon the adequacy or accuracy of this prospectus supplement or theaccompanying prospectus. Any representation to the contrary is a criminal offense. The Notes are not savings accounts, deposits or other obligations and will not be insured by the FDIC or any other governmental agencyor instrumentality, and they are not obligations of, or guaranteed by, our bank or any of our non-bank subsidiaries. TABLE OF CONTENTS PROSPECTUS SUPPLEMENT ABOUT THIS PROSPECTUS SUPPLEMENTS-iiINCORPORATION OF CERTAIN DOCUMENTS BY REFERENCES-iiiCAUTIONARY STATEMENT REGARDING FORWARD-LOOKING INFORMATIONS-vSUMMARYS-1THE OFFERINGS-3RISK FACTORSS-7USE OF PROCEEDSS-16CAPITALIZATIONS-17CONSOLIDATED CAPITAL RATIOSS-18DESCRIPTION OF THE NOTESS-19MATERIAL U.S. FEDERAL INCOME TAX CONSIDERATIONSS-37CERTAIN ERISA CONSIDERATIONSS-43UNDERWRITINGS-45VALIDITY OF NOTESS-48EXPERTSS-48 PROSPECTUS ABOUT THIS PROSPECTUS1CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING INFORMATION2WHERE YOU CAN FIND MORE INFORMATION4ABOUT THE CORPORATION4RISK FACTORS5USE OF PROCEEDS5PLAN OF DISTRIBUTION5SUMMARY OF THE SECURITIES WE MAY OFFER7VALIDITY OF THE SECURITIES8EXPERTS8 We have not, and the underwriter