By Pietro Lombardi

Sanofi SA will raise up to $11.7 billion by selling almost its entire 20.6% stake in U.S. biotech company Regeneron Pharmaceuticals Inc.

The French pharmaceutical major said late Tuesday that it is selling 11.8 million shares in the U.S. company at $515 each, while Regeneron will buy back $5 billion of its shares.

Sanofi has given the underwriters the option to buy up to 1.2 million additional shares.

After the two-part transaction, and assuming the option is fully exercised, Sanofi will keep 400,000 shares in the U.S. company, cashing $11.7 billion overall.

"Sanofi expects to use the net proceeds of the offering and the repurchase to further execute on its strategy to drive innovation and growth," it said.

Write to Pietro Lombardi at pietro.lombardi@dowjones.com