CONFIDENTIAL TREATMENT REQUESTED

                               FIRST AMENDMENT TO
                                 LEASE AGREEMENT

     This FIRST AMENDMENT TO LEASE AGREEMENT (the "First Amendment") is dated as
of April 1,  2000,  by and among  TEXAS  INSTRUMENTS  INCORPORATED,  a  Delaware
corporation   ("Lessor")  and  MEMC  SOUTHWEST  INC.,  a  Delaware   corporation
("Lessee"). All terms used herein, unless otherwise defined, shall have the same
meanings ascribed to them in the Lease (as defined below).

                                    Recitals

     WHEREAS,  Lessor  and  Lessee  made and  entered  into that  certain  Lease
Agreement  Covering Silicon Wafer Operations  Premises dated as of June 30, 1995
(the "Lease"); and

     WHEREAS, in connection with the [CONFIDENTIAL MATERIAL HAS BEEN DELETED AND
FILED  SEPARATELY WITH SEC],  Lessor and Lessee wish to amend the Lease to allow
for early termination by Lessee; and

     WHEREAS,  Article 35 of the Lease  allows the Lease to be amended  with the
written consent of Lessor and Lessee.

     NOW, THEREFORE, the parties agree as follows:

1.   The following shall be added at the end of Article 24:

     "Notwithstanding anything else to the contrary herein, effective January 1,
     2002,  Lessee  shall have the right to  terminate  this Lease upon at least
     twelve (12) months prior written  notice to Lessor.  In the event the Lease
     is  terminated  pursuant  to this  provision  prior  to the end of the then
     current term,  Lessee shall be responsible for all Rent up to and including
     the date of  termination.  Rent shall be prorated for any partial  month of
     occupancy  on the basis of 365 days per  year.  The  foregoing  termination
     shall be permitted  solely in connection  with  [CONFIDENTIAL  MATERIAL HAS
     BEEN DELETED AND FILED SEPARATELY WITH SEC]."

2.   Except as specifically  amended by this First Amendment,  all provisions of
     the Lease shall remain effective and binding. This Amendment, together with
     the Lease, constitutes the entire agreement between the Parties relating to
     the subject  matter  hereof and  supersedes  all prior  agreement,  oral or
     written, and all other communications between the Parties.

     IN WITNESS  WHEREOF,  the parties have executed this First  Amendment as of
the date first above  written and the terms herein shall be effective as of that
date.


Lessor:                                 Lessee:

TEXAS INSTRUMENTS INCORPORATED          MEMC SOUTHWEST INC.


By:  /s/ K. Balasubramanian             By:  /s/ James Lang
   ---------------------------             -------------------------------
Name:  K. Balasubramanian               Name:  James Lang
Title:  Senior Vice President           Title:  President