CONFIDENTIAL TREATMENT REQUESTED

                               FIRST AMENDMENT TO
                               SUBLEASE AGREEMENT


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

                                    Recitals

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

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

     WHEREAS,  Article 35 of the Sublease allows the Sublease to be amended with
the written consent of Sublessor and Sublessee.

     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,  Sublessee  shall have the right to terminate  this  Sublease upon at
     least twelve (12) months prior written  notice to  Sublessor.  In the event
     the Sublease is terminated  pursuant to this provision  prior to the end of
     the then current term,  Sublessee  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 Sublease shall remain effective and binding.  This Amendment,  together
     with the Sublease,  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.


Sublessor:                                      Sublessee:

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