The US Department of Justice (DoJ) has subpoenaed AMD and Nvidia as part of an anti-trust investigation into graphics processors and cards market.

AMD recently entered the graphics chip business with its acquisition of ATI Technologies, and the DoJ has not made any allegations against AMD or ATI. AMD said it will co-operate with the investigation.

Competing chip vendor Nvidia said on Friday that it had also received a subpoena, relating to an "investigation into potential anti-trust violations related to graphics processing units and cards." Nvidia said it would also co-operate with the order, which came from the DoJ's San Francisco office.

While the department hasn't said specifically what it is investigating, one industry analyst speculated that the case could be about price fixing. The DoJ has already charged a number of chip companies in the DRAM memory chip market for price fixing, and is investigating several in the SRAM chip market.

"If the DoJ wanted to, it could just go down every line in the semiconductor industry and find the same issue," said Gartner analyst Richard Gordon. That's because there are a relatively few number of suppliers in the chip industry and an open flow of communication between competitors and customers, who may not define price fixing the same way the DoJ does, he said.

The investigations are unlikely to benefit end users, according to Gordon. Historically, prices in the chip industry have gone up and down based on supply and demand and he doubts that such investigations will result in lower pricing.