The patent office "has now initially rejected all of the patent claims asserted by Rambus against Nvidia in the ITC," or U.S. International Trade Commission, Nvidia general counsel David Shannon said in a statement.

"The recent action by the (patent office) to re-examine Rambus patents is part of the process and Rambus will have an opportunity to respond," Rambus said.

Rambus, which has spent $300 million on legal disputes with chip makers since 2000, wants Nvidia to pay royalties on memory circuits used in Nvidia graphics chips.

The dispute began in June, 2008, when Rambus filed suit in federal court in San Francisco charging that Nvidia had infringed 17 patents. No dollar amount was attached to the suit, but Rambus has won millions in similar suits.