A day after losing an International Trade Commission patent dispute with STMicroelectronics ( STM), flash memory maker SanDisk ( SNDK) on Tuesday sued its rival in federal court over another patent. In a ruling against SanDisk, the U.S. ITC on Monday affirmed an administrative law judge's determination that certain STMicro's NAND flash memory chips do not infringe three claims of a SanDisk patent. Sunnyvale, Calif.-based SanDisk said it intends to appeal that decision to the U.S. Court of Appeals and argues that the order incorrectly interpreted the claims of the patent. Ratcheting up the legal tussle a bit, SanDisk also sued STMicroelectronics on Tuesday in the Northern District of California, charging that the Geneva-based company's NAND and NOR flash memory chips infringe on another SanDisk patent. "We really intend to vigorously defend ourselves and our IP portfolio," said SanDisk spokesman Mike Wong, noting the company's portfolio of 338 U.S. patents. STMicro spokeswoman Carol Brown declined to comment, citing company policy against commenting on ongoing litigation. Shares of SanDisk gained 98 cents, or 2%, to $49.54 in recent trading. Shares of STMicro recently increased 30 cents, or 1.6%, to $18.57.