CONFIDENTIAL TREATMENT REQUESTED

                               SECOND AMENDMENT TO
                            SHAREHOLDERS' AGREEMENT


     This SECOND AMENDMENT TO SHAREHOLDERS'  AGREEMENT (the "Second  Amendment")
is dated as of April 1, 2000,  by and among TEXAS  INSTRUMENTS  INCORPORATED,  a
Delaware  corporation  ("TI"),  MEMC  ELECTRONIC  MATERIALS,  INC.,  a  Delaware
corporation ("MEMC"),  and MEMC SOUTHWEST INC., a Delaware corporation ("NUCO").
All terms used herein,  unless otherwise  defined,  shall have the same meanings
ascribed to them in the Agreement (as defined below).

                                    Recitals

     WHEREAS,  TI and MEMC  made and  entered  into that  certain  Shareholders'
Agreement  dated as of May 16, 1995,  which was accepted and ratified by NUCO on
May 30, 1995, and amended by all parties on April 20, 1999 (the "Agreement");

     WHEREAS,  TI, MEMC and NUCO wish to amend the Agreement,  along with the TI
Purchase Agreement,  the Lease and the Sublease, for reasons stated in the First
Amendment to the TI Purchase Agreement ("First TI Purchase Amendment"); and

     WHEREAS,  Article 34 of the  Agreement  allows the  Agreement to be amended
with the written consent of TI, MEMC and NUCO.

     NOW, THEREFORE, the parties agree as follows:

1.   Section  11.02(a)(iii)  of the Agreement is deleted in its entirety and the
     following is substituted in lieu thereof:

          "(iii) restrict TI from practicing first level epi deposition at TI on
     Existing  Products  (as defined in the First TI Purchase  Amendment),  in a
     volume not to exceed  [CONFIDENTIAL  MATERIAL  HAS BEEN  DELETED  AND FILED
     SEPARATELY WITH SEC] per calendar  quarter  through 2003,  after which date
     first  level epi  deposition  by TI on  Existing  Products  will not exceed
     [CONFIDENTIAL MATERIAL HAS BEEN DELETED AND FILED SEPARATELY WITH SEC]"

2.   The following is added to Section 11.02(a)  immediately  preceding the last
     sentence thereof:

          "MEMC may elect at its  expense  to have TI's wafer  purchase  records
     audited by an independent third party acceptable to both parties to confirm
     the volumes set forth in (iii)  above.  In the event TI acquires  200mm epi
     reactors for the purpose of applying second level epi and  subsequently has
     excess   capacity,   TI  has  the  right  to  utilize  these  reactors  for
     [CONFIDENTIAL  MATERIAL  HAS BEEN  DELETED AND FILED  SEPARATELY  WITH SEC]
     first level epi  deposition on products  other than Existing  Products.  In
     addition,  if TI  contemplates  developing  capacity  for  first  level epi
     deposition  on  products  other than  Existing  Products,  MEMC and TI will
     negotiate in good faith a plan  determining  the method and timing in which
     TI may deposit first level epi on such other products."

3.   MEMC and TI agree that they will cause  their  representatives  on the NUCO
     Board of  Directors to approve  and/or  ratify this Second  Amendment,  the
     First TI Purchase  Amendment  and the  amendments to the Lease and Sublease
     referenced in the second "Whereas" clause above.  MEMC and TI further agree
     that the  implementation  of such amendments will be regularly  reviewed by
     the NUCO Board of Directors at their meetings.

4.   Except as specifically amended by this Second Amendment,  all provisions of
     the Agreement shall remain effective and binding. This Amendment,  together
     with the Agreement,  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.

5.   This Amendment shall be governed by the laws of the state of Texas, without
     regard to any conflicts of law principles  that may require the application
     of the laws of any other jurisdiction.

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


TEXAS INSTRUMENTS INCORPORATED          MEMC ELECTRONIC MATERIALS, INC.


By:  /s/ K. Balasubramanian             By:  /s/ Klaus R. von Horde
   -----------------------------           -----------------------------
Name:   K. Balasubramanian              Name:   Klaus R. von Horde
Title:  Senior Vice President           Title:  President and Chief Executive
                                                  Officer


MEMC SOUTHWEST INC.


By:  /s/ James Lang
   -----------------------------
Name: James Lang
Title:  President