FIRST SUPPLEMENTAL INDENTURE

Exhibit 4.2

FIRST SUPPLEMENTAL INDENTURE

Dated as of May 18, 2009

to

INDENTURE

Dated as of May 18, 2009

Between

MICROSOFT CORPORATION,

as Issuer

and

THE BANK OF NEW YORK MELLON TRUST COMPANY, N.A.,

as Trustee

2.95% Notes due 2014

4.20% Notes due 2019

5.20% Notes due 2039

TABLE OF CONTENTS

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FIRST SUPPLEMENTAL INDENTURE, dated as of May 18, 2009 (this “ Supplemental Indenture ”), between MICROSOFT CORPORATION, a corporation duly organized and existing under the laws of the State of Washington (the “ Company ”), and THE BANK OF NEW YORK MELLON TRUST COMPANY, N.A., a national banking association duly organized and existing under the laws of the United States, as Trustee (the “ Trustee ”).

RECITALS OF THE COMPANY

WHEREAS, the Company executed and delivered the Indenture, dated as of May 18, 2009, to the Trustee (the “ Indenture ”), to provide for the issuance of the Company’s debt securities (the “ Securities ”), to be issued in one or more series;

WHEREAS, pursuant to the terms of the Indenture, the Company desires to provide for the establishment of three new series of its Securities under the Indenture to be known as its “2.95% Notes due 2014” (the “ 2014 Notes ”), “4.20% Notes due 2019” (the “ 2019 Notes ”) and “5.20% Notes due 2039” (the “ 2039 Notes ” and, together with the 2014 Notes and the 2019 Notes, the “ Notes ”), the form and substance and the terms, provisions and conditions thereof to be set forth as provided in the Indenture and this Supplemental Indenture;

WHEREAS, the Board of Directors of the Company by duly adopted resolutions has authorized the proper officers of the Company to, among other things, determine the terms of the Securities to be issued under the Indenture and execute any and all appropriate documents necessary or appropriate to effect each such issuance;

WHEREAS, this Supplemental Indenture is being entered into pursuant to the provisions of Section 901(7) of the Indenture;

WHEREAS, the Company has requested that the Trustee execute and deliver this Supplemental Indenture; and

WHEREAS, all things necessary to make this Supplemental Indenture a valid agreement of the Company, in accordance with its terms, and to make the Notes, when executed by the Company and authenticated and delivered by the Trustee, the valid obligations of the Company, have been performed, and the execution and delivery of this Supplemental Indenture has been duly authorized in all respects;

NOW, THEREFORE, THIS SUPPLEMENTAL INDENTURE WITNESSETH:

For and in consideration of the premises and the purchase of the Notes by the Holders thereof, and for the purpose of setting forth, as provided in the Indenture, the forms and terms of the Notes, the Company covenants and agrees, with the Trustee, as follows:

ARTICLE 1.

DEFINITIONS

Section 1.1. Definition of Terms . Unless the context otherwise requires:

(a) each term defined in the Indenture has the same meaning when used in this Supplemental Indenture;

(b) the singular includes the plural, and vice versa ; and

(c) headings are for convenience of reference only and do not affect interpretation.

ARTICLE 2.

TERMS AND CONDITIONS OF NOTES

Section 2.1. Designation and Principal Amount .

(a) There is hereby authorized and established a series of Securities under the Indenture, designated as the “2.95% Notes due 2014,” which is initially limited in aggregate principal amount to $2,000,000,000 (except upon registration of transfer of, or in exchange for, or in lieu of, other 2014 Notes pursuant to Section 304, 305, 306, 906 or 1107 of the Indenture and except for any Securities which, pursuant to Section 303 of the Indenture, are deemed never to have been authenticated and delivered).

(b) There is hereby authorized and established a series of Securities under the Indenture, designated as the “4.20% Notes due 2019,” which is initially limited in aggregate principal amount to $1,000,000,000 (except upon registration of transfer of, or in exchange for, or in lieu of, other 2019 Notes pursuant to Section 304, 305, 306, 906 or 1107 of the Indenture and except for any Securities which, pursuant to Section 303 of the Indenture, are deemed never to have been authenticated and delivered).

(c) There is hereby authorized and established a series of Securities under the Indenture, designated as the “5.20% Notes due 2039,” which is initially limited in aggregate principal amount to $750,000,000 (except upon registration of transfer of, or in exchange for, or in lieu of, other 2039 Notes pursuant to Section 304, 305, 306, 906 or 1107 of the Indenture and except for any Securities which, pursuant to Section 303 of the Indenture, are deemed never to have been authenticated and delivered).

Section 2.2. Maturity .

(a) The Stated Maturity of principal of the 2014 Notes shall be June 1, 2014.

(b) The Stated Maturity of principal of the 2019 Notes shall be June 1, 2019.

(c) The Stated Maturity of principal of the 2039 Notes shall be June 1, 2039.

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Section 2.3. Further Issues . The Company may at any time and from time to time, without the consent of the Holders of any series of the Notes, issue additional notes of any series. Any such additional notes shall have the same ranking, interest rate, maturity date and other terms as the relevant series of the Notes. Any such additional notes of a series, together with the Notes of the relevant series herein provided for, shall constitute a single series of Securities under the Indenture.

Section 2.4. Payment . Principal of and interest on the Notes shall be payable in U.S. dollars in immediately available funds at the office or agency of the Company maintained for such purpose in New York, New York, which shall initially be at an office of the Trustee located at 101 Barclay Street, 8W, New York, New York 10286, Attention: Corporate Trust Administration; provided , however , that payment of interest may be made at the option of the Company by check mailed to the Holder at such address as shall appear in the Security Register at the close of business on the Record Date for such Holder or by wire transfer to an account appropriately designated by the Holder to the Company and the Trustee; and provided , further , that the Company will pay principal of and interest on, the Notes in global form registered in the name of or held by The Depository Trust Company (“ DTC ”) or such other Depositary as any Officer of the Company may from time to time designate, or its respective nominee, by wire in immediately available funds to such Depositary or its nominee, as the case may be, as the registered holder of such Notes in global form.

Section 2.5. Global Securities . Upon the original issuance, the Notes will be represented by Global Securities registered in the name of Cede & Co., the nominee of DTC. The Company will deposit the Global Securities with DTC or its custodian and register the Global Securities in the name of Cede & Co.

Section 2.6. Interest .

(a) The 2014 Notes will bear interest (computed on the basis of a 360-day year consisting of twelve 30-day months) from May 18, 2009 at the rate of 2.95% per annum, payable semi-annually in arrears. Interest payable on each Interest Payment Date will include interest accrued from May 18, 2009, or from the most recent Interest Payment Date to which interest has been paid or duly provided for. The Interest Payment Dates on which such interest shall be payable are June 1 and December 1, commencing on December 1, 2009; and the Record Date for the interest payable on any Interest Payment Date is the close of business on May 15 or November 15, as the case may be, next preceding the relevant Interest Payment Date.

(b) The 2019 Notes will bear interest (computed on the basis of a 360-day year consisting of twelve 30-day months) from May 18, 2009 at the rate of 4.20% per annum, payable semi-annually in arrears. Interest payable on each Interest Payment Date will include interest accrued from May 18, 2009, or from the most recent Interest Payment Date to which interest has been paid or duly provided for. The Interest Payment Dates on which such interest shall be payable are June 1 and December 1, commencing on December 1, 2009; and the Record Date for the interest payable on any Interest Payment Date is the close of business on May 15 or November 15, as the case may be, next preceding the relevant Interest Payment Date.

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(c) The 2039 Notes will bear interest (computed on the basis of a 360-day year consisting of twelve 30-day months) from May 18, 2009 at the rate of 5.20% per annum, payable semi-annually in arrears. Interest payable on each Interest Payment Date will include interest accrued from May 18, 2009, or from the most recent Interest Payment Date to which interest has been paid or duly provided for. The Interest Payment Dates on which such interest shall be payable are June 1 and December 1, commencing on December 1, 2009; and the Record Date for the interest payable on any Interest Payment Date is the close of business on May 15 or November 15, as the case may be, next preceding the relevant Interest Payment Date.

Section 2.7. Authorized Denominations . The Notes shall be issuable in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

Section 2.8. Redemption and Sinking Fund . The Notes shall not be redeemable at the option of the Company or at the option of the Holders. The Notes shall not be entitled to the benefit of any sinking fund.

Section 2.9. Ranking . The Notes shall be senior unsecured debt securities of the Company, ranking equally with the Company’s other unsecured and unsubordinated debt.

Section 2.10. Appointments . The Trustee will be the initial Security Registrar and initial Paying Agent for the Notes.

Section 2.11. Defeasance . The Company may elect, at its option at any time, pursuant to Section 1301 of the Indenture, to have Section 1302 or Section 1303 in the Indenture, or both, apply to the 2014 Notes, the 2019 Notes or the 2039 Notes, or all, or any principal amount thereof.

ARTICLE 3.

FORM OF NOTES

Section 3.1. Form of Notes . The Notes and the Trustee’s Certificate of Authentication to be endorsed thereon are to be substantially in the forms set forth in Exhibits A, B and C hereto.

ARTICLE 4.

ORIGINAL ISSUE OF NOTES

Section 4.1. Original Issue of Notes . The Notes may, upon execution of this Supplemental Indenture, be executed by the Company and delivered to the Trustee for authentication, and the Trustee shall, upon Company Order, authenticate and deliver such Notes as in such Company Order provided.

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ARTICLE 5.

MISCELLANEOUS

Section 5.1. Ratification of Indenture . The Indenture, as supplemented by this Supplemental Indenture, is in all respects ratified and confirmed, and this Supplemental Indenture shall be deemed part of the Indenture in the manner and to the extent herein and therein provided; provided , however , that the provisions of this Supplemental Indenture shall apply solely with respect to the Notes.

Section 5.2. Trustee Not Responsible for Recitals . The recitals herein contained are made by the Company and not by the Trustee, and the Trustee assumes no responsibility for the correctness thereof. The Trustee makes no representation as to the validity or sufficiency of this Supplemental Indenture.

Section 5.3. Governing Law . This Supplemental Indenture and each Note shall be governed by, and construed in accordance with, the laws of the State of New York.

Section 5.4. Separability . In case any one or more of the provisions contained in the Indenture, this Supplemental Indenture or the Notes shall for any reason be held to be invalid, illegal or unenforceable in any respect, such invalidity, illegality or unenforceability shall not affect any other provisions of the Indenture, this Supplemental Indenture or the Notes, but the Indenture, this Supplemental Indenture and the Notes shall be construed as if such invalid or illegal or unenforceable provision had never been contained herein or therein.

Section 5.5. Counterparts . This Supplemental Indenture may be executed in any number of counterparts each of which shall be an original; but such counterparts shall together constitute but one and the same instrument.

[ Signature page follows ]

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IN WITNESS WHEREOF, the parties hereto have caused this First Supplemental Indenture to be duly executed, all as of the day and year first above written.

EXHIBIT A

[FORM OF NOTE]

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“ DTC ”), NEW YORK, NEW YORK, TO THE COMPANY OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE INDENTURE REFERRED TO ON THE REVERSE HEREOF.

THIS NOTE IS A GLOBAL SECURITY WITHIN THE MEANING OF THE INDENTURE REFERRED TO HEREIN AND IS REGISTERED IN THE NAME OF A DEPOSITARY OR A NOMINEE THEREOF. THIS NOTE MAY NOT BE EXCHANGED IN WHOLE OR IN PART FOR A NOTE REGISTERED, AND NO TRANSFER OF THIS NOTE IN WHOLE OR IN PART MAY BE REGISTERED, IN THE NAME OF ANY PERSON OTHER THAN SUCH DEPOSITARY OR A NOMINEE THEREOF, EXCEPT IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE.

MICROSOFT CORPORATION

2.95% Notes due 2014

CUSIP No.: 594918 AB0

ISIN: US594918AB00

MICROSOFT CORPORATION, a corporation duly incorporated under the laws of the State of Washington (herein called the “ Company ,” which term includes any successor Person under the Indenture hereinafter referred to), for value received, hereby promises to pay to CEDE & CO., or registered assigns, the principal sum of $500,000,000 (FIVE HUNDRED MILLION DOLLARS) on June 1, 2014, and to pay interest thereon from May 18, 2009 or from the most

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recent Interest Payment Date to which interest has been paid or duly provided for, semi-annually on June 1 and December 1 of each year, commencing on December 1, 2009, at the rate of 2.95% per annum, until the principal hereof is paid or made available for payment; provided that any principal and premium, and any such installment of interest, which is overdue shall bear interest at the rate of 2.95% per annum (to the extent permitted by applicable law), from the dates such amounts are due until they are paid or made available for payment, and such interest shall be payable on demand. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Note (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be the May 15 or November 15 (whether or not a Business Day), as the case may be, next preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the Holder