<PAGE>
                                                                   EXHIBIT 4.2.6

                               AMENDMENT NO. 6 TO

                        PREFERRED SHARES RIGHTS AGREEMENT


     This AMENDMENT NO. 6 TO PREFERRED SHARES RIGHTS AGREEMENT dated as of June
18, 2004 (the "Amendment") is made by and between Catalyst Semiconductor, Inc.,
a Delaware corporation (the "Company") and EquiServe Trust Company, N.A., as
rights agent (the "Rights Agent").

                                    RECITALS

     WHEREAS, the Company and the Rights Agent are parties to a Preferred Shares
Rights Agreement dated as of December 3, 1996, as amended (the "Rights
Agreement");

     WHEREAS, in connection with the sale by Elex N.V. of shares of the
Company's Common Stock in a firm commitment public offering, and pursuant to
Section 27 of the Rights Agreement, the Board of Directors of the Company has
determined that an amendment to the Rights Agreement to remove certain
exceptions applicable to Elex N.V., Roland Duchatelet and their respective
Affiliates and Associates, as set forth herein, is necessary and desirable, and
the Company and the Rights Agent desire to evidence such amendment in writing.

     NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the Company and the Rights Agent
hereby agree as follows:

     1. Amendment of Section 1(a). Section 1(a) of the Rights Agreement is
hereby amended in its entirety to read as follows:

          "(a) "ACQUIRING PERSON" shall mean any Person who or which, together
     with all Affiliates and Associates of such Person, shall be the Beneficial
     Owner of 15% or more of the Common Shares then outstanding, but shall not
     include the Company, any Subsidiary of the Company or any employee benefit
     plan of the Company or of any Subsidiary of the Company, or any entity
     holding Common Shares for or pursuant to the terms of any such plan.
     Notwithstanding the foregoing, no Person shall be deemed to be an Acquiring
     Person: (i) as the result of an acquisition of Common Shares by the Company
     which, by reducing the number of shares outstanding, increases the
     proportionate number of shares beneficially owned by such Person to 15% or
     more of the Common Shares of the Company then outstanding; provided,
     however, that if a Person shall become the Beneficial Owner of 15% or more
     of the Common Shares of the Company then outstanding by reason of share
     purchases by the Company and shall, after such share purchases by the
     Company, become the Beneficial Owner of any additional Common Shares of the
     Company, then such Person shall be deemed to be an Acquiring Person, or
     (ii) if within eight days after such Person would otherwise become an
     Acquiring Person (but for the operation of this clause (ii)), such Person
     notifies the Board of Directors that such Person did so inadvertently and
     within two


<PAGE>

     days after such notification, such Person is the Beneficial Owner of less
     than 15% of the outstanding Common Shares."

     2. Effectiveness. This Amendment shall be deemed effective immediately
prior to the time the Registration Statement (as defined below) is declared
effective by the United States Securities and Exchange Commission. In the event
the Registration Statement has not been declared effective by September 30,
2004, this Amendment shall be of no force or effect. For purposes hereof,
"Registration Statement" shall mean the registration statement on Form S-3 filed
by the Company with the United States Securities and Exchange Commission on June
14, 2004, which includes shares of the common stock held by Elex N.V. as a
portion of the shares to be sold pursuant to such registration statement.

     3. Confirmation of Rights Agreement. Except as specifically amended hereby,
all of the terms of the Rights Agreement shall remain and continue in full force
and effect and are hereby confirmed in all respects.

     4. Counterparts. This Amendment may be executed in counterparts and the
signature pages may be combined to create a document binding on all of the
parties hereto.

     5. Miscellaneous. This Amendment shall be deemed to be a contract made
under the laws of the State of Delaware and for all purposes shall be governed
by and construed in accordance with the laws of such state applicable to
contracts to be made and performed entirely within such state. This Amendment
may be executed in any number of counterparts, each of such counterparts shall
for all purposes be deemed to be an original, and all such counterparts shall
together constitute but one and the same instrument. If any provision, covenant
or restriction of this Amendment is held by a court of competent jurisdiction or
other authority to be invalid, illegal or unenforceable, the remainder of the
terms, provisions, covenants and restrictions of this Amendment shall remain in
full force and effect and shall in no way be affected, impaired or invalidated.



                  (REMAINDER OF PAGE LEFT BLANK INTENTIONALLY)



<PAGE>

     IN WITNESS WHEREOF, the undersigned have caused their duly authorized
representatives to execute this Amendment as of the date first written above.




                                   CATALYST SEMICONDUCTOR, INC.



                                   By: /s/ Thomas E. Gay III
                                       ---------------------------------------
                                       Thomas E. Gay III
                                       Vice President of Finance and
                                       Administration and Chief Financial
                                       Officer



                                    EQUISERVE TRUST COMPANY N.A.



                                    By:  /s/ Carol Mulvey-Eori
                                         -------------------------
                                         Name: Carol Mulvey-Eori
                                         Title: Managing Director