Limited Power of Attorney - Securities Law Compliance

I, as an officer or director of Silicon Valley Bancshares
and subsidiaries ("SVB"), appoint Derek Witte, Grace Leung
and Lisa Bertolet, and each of them, my true and lawful
attorney-in-fact and agent to complete and execute Forms 144,
Forms 3, 4 and 5 and other forms as the attorney determines
in his or her discretion to be required or advisable pursuant
to Rule 144 under the Securities Act of 1933 (as amended),
Section 16 of the Securities Exchange Act of 1934 (as amended)
and its rules and regulations, or any successor laws and
regulations, as a consequence of my ownership, acquisition
or disposition of securities of SVB, and to do all acts
necessary in order to file my forms with the Securities
and Exchange Commission, any securities exchange or national
association, SVB and other person or agency as the attorney
deems appropriate.  I ratify and confirm all that the
attorneys-in-fact and agents do or cause to be done.

This Limited Power of Attorney is executed in Palo Alto, CA
as of the date below and shall remain effective until
July 31, 2004, unless I am no longer required to complete
said forms.



Signature   (s) Larry W. Sonsini
            ____________________

Type or Print Name:  Larry W. Sonsini
Dated:  November 17, 2003


Witness:

Signature:  (s) Lisa Gomes
            ______________

Type or Print Name:  Lisa Gomes
Dated:  November 17, 2003