Exhibit
31.2


Certifications Under Rule
13a-14(a)/l5d-14(a)





I, Phillip A. Kagel, certify
that:





1.             I
have reviewed this quarterly report on Form 10-Q of Supertex, Inc., a California
corporation;





2.             Based
on my knowledge, this quarterly report does not contain any untrue statement of
a material fact or omit to state a material fact necessary to make the
statements made, in light of the circumstances under which such statements were
made, not misleading with respect to the period covered by this quarterly
report;





3.             Based
on my knowledge, the financial statements, and other financial information
included in this quarterly report, fairly present in all material respects the
financial condition, results of operations and cash flows of the registrant as
of, and for, the periods presented in this quarterly report;





4.             The
registrant’s other certifying officer and I are responsible for establishing and
maintaining disclosure controls and procedures (as defined in Exchange Act Rules
13a-15(e) and 15d-15(e)) and internal control over financial reporting (as
defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and I
have:





(a)                               designed
such disclosure controls and procedures, or caused such disclosure controls and
procedures to be designed under our supervision, to ensure that material
information relating to the registrant, including its consolidated subsidiaries,
is made known to me by others within those entities, particularly during the
period in which this quarterly report is being prepared;





(b)   designed such
internal control over financial reporting, or caused such internal control over
financial reporting to be designed under our supervision, to provide reasonable
assurance regarding the reliability of financial reporting and the preparation
of financial statements for external purposes in accordance with GAAP;





(c)                               evaluated
the effectiveness of the registrant's disclosure controls and procedures and
presented in this report our conclusion about the effectiveness of the
disclosure controls and procedures, as of the end of the period covered by this
report based on such evaluation; and





(d)                               disclosed
in this report any change in the registrant’s internal control over financial
reporting that occurred during the registrant’s most recent fiscal quarter that
has materially affected, or is reasonably likely to materially affect, the
registrant’s internal control over financial reporting; and





5.             The
registrant’s other certifying officer and I have disclosed, based on our most
recent evaluation of internal control over financial reporting, to the
registrant's auditors and the audit committee of registrant's board of directors
(or persons performing the equivalent function):





(a)                               all
significant deficiencies and material weaknesses in the design or operation of
internal control over financial reporting which are reasonably likely to
adversely affect the registrant's ability to record, process, summarize, and
report financial data and have identified for the registrant's auditors any
material weaknesses in internal controls; and





(b)                               any
fraud, whether or not material, that involves management or other employees who
have a significant role in the registrant's internal controlover financial
reporting.





Dated:  November
      5, 2008
              
              
              /s/PHILLIP A.
      KAGELPhillip
      A. KagelVice
      President, Finance and Chief Financial Officer(Principal
      Financial and Accounting
Officer)