Microsoft (MSFT) S-4Registration of securities issued in business combination transactions

Exhibit 5.1

Simpson Thacher & BartlettLLP

2475HANOVERSTREET

PALOALTO,CA 94304

TELEPHONE: +1-650-251-5000

FACSIMILE: +1-650-251-5002

April 26, 2024

Microsoft Corporation

One Microsoft Way

Redmond, Washington 98052-6399

Ladies and Gentlemen:

We have acted as counsel to Microsoft Corporation, a Washington corporation (the “Company”), in connection with the Registration Statement on Form S-4 (the “Registration Statement”) filed by the Company with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended, relating to the issuance of up to $3,400,683,000 in aggregate principal amount of new series of notes of the Company (the “Registered Notes”) pursuant to the exchange offers (the “Exchange Offers”) described in the Registration Statement. Upon the terms and subject to the conditions set forth in the prospectus contained in the Registration Statement (the “Prospectus”), the Company is offering to exchange the notes of the Company set forth on Annex I hereto (the “Restricted Notes”) for Registered Notes, as applicable and as set forth on Annex I hereto. The Registered Notes will be issued under the indenture, dated as of May 18, 2009 (the “Base Indenture”), between the Company and The Bank of New York Mellon Trust Company, N.A., as trustee (the “Trustee”), as amended and supplemented by the fifteenth supplemental indenture thereto, dated as of November 6, 2023 (the “Fifteenth Supplemental Indenture” and, together with the Base Indenture, the “Indenture”), between the Company and the Trustee.

We have examined the Registration Statement and the Base Indenture, the Fifteenth Supplemental Indenture and the forms of the Registered Notes, each an exhibit to the Registration Statement. In addition, we have examined, and have relied as to matters of fact upon, originals, or duplicates or certified or conformed copies, of such records, agreements, documents and other instruments and such certificates or comparable documents of public officials and of officers and representatives of the Company and have made such other investigations as we have deemed relevant and necessary in connection with the opinion hereinafter set forth.

In rendering the opinion set forth below, we have assumed the genuineness of all signatures, the legal capacity of natural persons, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as duplicates or certified or conformed copies and the authenticity of the originals of such latter documents. We also have assumed that at the time of execution, authentication, issuance and delivery of the Registered Notes, the Indenture will be the valid and legally binding obligation of the Trustee.

In rendering the opinion set forth below, we have assumed further that, at the time of execution, authentication, issuance and delivery, as applicable, of the Registered Notes, (i) the Company will be validly existing and in good standing under the law of the jurisdiction in which it is organized and the Registered Notes will have been duly executed and delivered by the Company in accordance with its organizational documents and the law of the jurisdiction in which it is organized, (ii) the execution, issuance, delivery and performance by the Company of the Registered Notes and the Indenture, as applicable, will not constitute a breach or violation of its organizational documents or violate the law of the jurisdiction in which it is organized or any other jurisdiction (except that no such assumption is made with respect to the law of the State of New York, assuming there shall not have been any changes in such law affecting the validity or enforceability of the Indenture) and (iii) the execution, issuance, delivery and performance by the Company of the Registered Notes and the Indenture, as applicable, will not constitute a breach or default under any agreement or instrument which is binding upon the Company.

In rendering the opinion set forth below, we have assumed further that (i) the Registration Statement and any supplements and amendments thereto (including post-effective amendments) will have become effective and will comply with all applicable laws; (ii) the Registration Statement and any supplements and amendments thereto (including post-effective amendments) will be effective and will comply with all applicable laws at the time the Registered Notes are offered or issued as contemplated by the Registration Statement; and (iii) all Registered Notes will be issued and sold in compliance with applicable federal and state securities laws and in the manner stated in the Registration Statement and the Prospectus.

Based upon the foregoing, and subject to the qualifications, assumptions and limitations stated herein, we are of the opinion that, when the Registered Notes have been duly executed, authenticated, issued and delivered in accordance with the Indenture pursuant to the Exchange Offers, the Registered Notes will constitute valid and legally binding obligations of the Company enforceable against the Company in accordance with their terms.

Our opinion set forth above is subject to (i) the effects of bankruptcy, insolvency, fraudulent conveyance, reorganization, moratorium and other similar laws relating to or affecting creditors’ rights generally, (ii) general equitable principles (whether considered in a proceeding in equity or at law) and (iii) an implied covenant of good faith and fair dealing. In addition, we express no opinion as to the validity, legally binding effect or enforceability of Section 110 of the Base Indenture or Section 5.4 of the Fifteenth Supplemental Indenture relating to the separability of provisions of the Base Indenture, the Fifteenth Supplemental Indenture and the Registered Notes, as applicable.

Insofar as the opinion expressed herein relates to or is dependent upon matters governed by the law of the State of Washington, we have relied, without any independent investigation, upon the opinion of Keith R. Dolliver, Esq., Deputy General Counsel and Corporate Secretary of the Company, dated the date hereof, filed as an exhibit to the Registration Statement, and our opinion is subject to the qualifications, assumptions, limitations and exceptions set forth therein.

We do not express any opinion herein concerning any law other than the law of the State of New York and, to the extent set forth herein, the law of the State of Washington.

We hereby consent to the filing of this opinion letter as Exhibit 5.1 to the Registration Statement filed with the Commission and to the use of our name under the caption “Legal Matters” in the Prospectus included in the Registration Statement.

Very truly yours,

/s/ Simpson Thacher & Bartlett LLP

SIMPSON THACHER & BARTLETT LLP

Annex I