REVOLVING CREDIT AGREEMENT

Exhibit 10.42

Execution Version

MEMC ELECTRONIC MATERIALS, INC.

as the Borrower

THE LENDING INSTITUTIONS NAMED HEREIN

as Lenders

and

NATIONAL CITY BANK,

as a Lender, the Swing Line Lender, the Issuing Bank,

the Administrative Agent and the Collateral Agent

AMENDMENT NO. 1

dated as of

December 20, 2006,

to

REVOLVING CREDIT AGREEMENT

dated as of

July 21, 2005

AMENDMENT NO. 1

THIS AMENDMENT NO. 1 (this “ Amendment ”) is entered into as of December 20, 2006 (the “ Amendment Closing Date ”), among the following:

(i) MEMC ELECTRONIC MATERIALS, INC. , a Delaware corporation (herein, together with its successors and assigns, the “Borrower ”);

(ii) the lending institutions signatory hereto (herein, together with their successors and assigns, each a “ Lender ” and collectively, the “ Lenders ”); and

(iii) NATIONAL CITY BANK , a national banking association (successor to National City Bank of the Midwest), as a Lender, the Swing Line Lender, the Issuing Bank, and as the administrative agent (the “ Administrative Agent ”), the collateral agent (the “ Collateral Agent ”).

PRELIMINARY STATEMENTS:

A. The Borrower, the Lenders and the Administrative Agent entered into the Revolving Credit Agreement, dated as of July 21, 2005 (the “ Credit Agreement ”). All capitalized terms used in this Amendment but not otherwise defined shall have the meanings given to such terms in the Credit Agreement.

B. In connection with the Credit Agreement, the Borrower, the Subsidiary Guarantors and the Collateral Agent executed the Pledge Agreement, dated as of July 21, 2005 (the “ Pledge Agreement ”).

C. The parties hereto desire to amend certain provisions of the Credit Agreement and terminate the Pledge Agreement, as more fully set forth below.

NOW, THEREFORE, for good and valuable consideration, the receipt and sufficiency of which is hereby acknowledged, the parties hereto agree as follows:

SECTION 1. AMENDMENTS & TERMINATION. Effective on and as of the Amendment Effective Date (as defined in Section 2 of this Amendment):

1.1 AMENDMENT TO SCHEDULE 1. Schedule 1 to the Credit Agreement shall be amended and restated as set forth at Exhibit A to this Amendment.

1.2 AMENDMENT OF SECTION 1.1. The definition of “ Additional Security Document ” is hereby deleted from Section 1.1 of the Credit Agreement.

1.3 AMENDMENT OF SECTION 2.7(F). Section 2.7(f) of the Credit Agreement is hereby amended and restated as follows:

(f) Interest Rate Margins. As used herein the terms “ Applicable Prime Rate Margin ”, “ Applicable Eurocurrency Margin ” and “ Applicable Commitment Fee Rate ” shall mean the particular rate per annum determined by the Administrative Agent in accordance with the Pricing Grid Table which appears below, based on the Borrower’s ratio of Consolidated Total Funded Debt as of the end of each fiscal quarter to Consolidated EBITDA for the Testing Period most recently ended and the following provisions:

(A) On the Amendment Effective Date, until changed hereunder in accordance with the following provisions, the Applicable Prime Rate Margin for Revolving Loans and Swing Line Loans will be 0.00 basis points per annum, the Applicable Eurocurrency Margin for Revolving Loans will be 34.00 basis points per annum, and the Applicable Commitment Fee Rate shall be 8.00 basis points per annum.

(B) Commencing with the fiscal quarter of the Borrower ended on or nearest to December 31, 2006, and continuing with each fiscal quarter thereafter, the Administrative Agent will determine the Applicable Prime Rate Margin or Applicable Eurocurrency Margin for any Revolving Loan or Swing Line Loan and the Applicable Commitment Fee Rate in accordance with the Pricing Grid Table, based on the Borrower’s ratio of (x) Consolidated Total Funded Debt as of the end of the fiscal quarter, to (y) Consolidated EBITDA for the Testing Period ended on the last day of the fiscal quarter, as identified in such Pricing Grid Table. Changes in the Applicable Prime Rate Margin, Applicable Eurocurrency Margin or Applicable Commitment Fee Rate based upon changes in such ratio shall become effective on the first day of the month following the receipt by the Administrative Agent pursuant to section 8.1(a) or (b) of the financial statements of the Borrower, accompanied by the certificate and calculations referred to in section 8.1(c), demonstrating the computation of such ratio, based upon the ratio in effect at the end of the applicable period covered (in whole or in part) by such financial statements.

(C) Notwithstanding the above provisions, during any period when (1) the Borrower has failed to timely deliver its consolidated financial statements referred to in section 8.1(a) or (b), accompanied by the certificate and calculations referred to in section 8.1(c) or (2) an Event of Default has occurred and is continuing, the Applicable Prime Rate Margin and the Applicable Eurocurrency Margin for Revolving Loans and Swing Line Loans and the Applicable Commitment Fee Rate shall be the highest rate per annum indicated therefor in the Pricing Grid Table, regardless of the Borrower’s ratio of Consolidated Total Debt to Consolidated EBITDA at such time.

(D) Any changes in the Applicable Prime Rate Margin or Applicable Eurocurrency Margin for Revolving Loans or Swing Line Loans and the Applicable Commitment Fee Rate shall be determined by the Administrative Agent in accordance with the above provisions and the Administrative Agent will promptly provide notice of such determinations to the Borrower and the Lenders. Any such determination by the Administrative Agent pursuant to this section 2.7(f) shall be conclusive and binding absent manifest error.

PRICING GRID TABLE

(Expressed in Basis Points)

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1.4 AMENDMENT OF SECTION 4.1. Section 4.1(a) of the Credit Agreement shall be amended and restated as follows:

4.1(a) Commitment Fees. The Borrower agrees to pay to the Administrative Agent fees (“ Commitment Fees ”) for the account of each Non-Defaulting Lender for the period from and including the Amendment Effective Date to, but not including, the Maturity Date or, if earlier, the date upon which the Total Revolving Commitment has been terminated, computed for each day at a rate per annum equal to the Applicable Commitment Fee Rate for such day on the amount of such Lender’s Revolving Commitment for such day. Commitment Fees shall be due and payable in arrears on April 1, July 1, October 1 and January 1 and on the Maturity Date or, if earlier, the date upon which the Total Revolving Commitment has been terminated.

1.5 AMENDMENT TO SCHEDULE 7.2. Schedule 7.2 to the Credit Agreement shall be amended and restated as set forth at Exhibit B to this Amendment.

1.6 AMENDMENT OF SECTION 8.12. Section 8.12 of the Credit Agreement shall be deleted in its entirety and replaced with the following:

8.12 [Reserved].

1.7 AMENDMENT OF SECTION 9.2. The last paragraph of Section 9.2 of the Credit Agreement shall be amended and restated as follows:

With respect to any Subsidiary which is a party to the Subsidiary Guaranty, such Subsidiary shall be released from the Subsidiary Guaranty if all of such Subsidiary’s capital stock (or other equity interests) are disposed of in accordance with this Section 9.2; and the Administrative Agent and the Collateral Agent shall be authorized to take actions deemed appropriate by them in order to effectuate the foregoing.

1.8 AMENDMENT OF SECTION 9.4. Section 9.4 of the Credit Agreement shall be amended by adding an additional subclause (j) as follows:

(j) Existing Letter of Credit: the letter of credit in the face amount of $2,550,000 issued by U.S. Bank, National Association for the benefit of the Missouri Department of Natural Resources having a letter of credit number of SLCL120281 and an annual expiration date of June 9th with automatic annual extensions.

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1.9 TERMINATION OF PLEDGE AGREEMENT. Notwithstanding Sections 7.19 and 10.1(f) of the Credit Agreement, the Pledge Agreement shall be terminated and shall be of no further force and effect and all Pledged Stock and Pledged Equity Interests (each as defined in the Pledge Agreement) shall be promptly returned to the Borrower by the Collateral Agent. The termination of the Pledge Agreement pursuant to this Amendment shall not constitute a breach of the representation set forth in Section 7.19 of the Credit Agreement now or subsequent to the date hereof, and such termination shall not constitute a Default or an Event of Default pursuant to Section 10.1(f) of the Credit Agreement.

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