Tom Siebel, the chairman of

Siebel Systems

(SEBL)

, plans to sell up to 10 million shares of the company's stock over an 18-month period beginning around February, the company said.

Siebel, who turned over the CEO reins to Mike Lawrie earlier this year, plans the divestiture for diversification purposes. If he sells 10 million Siebel Systems shares, he will be left with about 45 million shares and options, or about 9% of its outstanding total. Siebel has about 500 million shares outstanding.

The sale "will commence no earlier than February 2005 and will be disclosed publicly through filings with the

Securities and Exchange Commission

," Siebel said. Some of the shares will be acquired through the exercising of stock options, Siebel said, including options that are set to expire on their 10-year anniversary in March 2006.

Siebel closed Monday at $9.44.