Leading Dynamic RAM (DRam) makers have been ordered to provide information to the US Department of Justice in its investigation into alleged anticompetitive practices.
According to The Wall Street Journal, Micron Technology and Samsung Electronics have received a subpoena.
In a brief statement, Micron, the largest manufacturer of DRam chips in the US, said it intended to co-operate fully with the investigation.
The statement said: "Micron does not believe it has violated US antitrust laws. The DRam business is highly competitive and subject to extreme volatility. Competitive forces in today's market have led to DRam prices reaching unprecedented lows."
Samsung has yet to comment on the news.
The price of DRam chips is always changing and last began a gradual decline from about $9 per 128MB chip to an all-time low of $1.50 per chip in the third quarter.
But analysts and some memory makers said the price was well below cost price and that manufacturers were staying in the market to protect their share in anticipation of an upturn.
Meanwhile, US antitrust enforcers have accused Rambus of obtaining patent royalties for its high-speed memory chip designs by deceit.
The Federal Trade Commission (FTC) has approved a complaint charging that the company failed to disclose its patent applications to an industry group that was setting memory chip standards and then demanded royalties from the world's largest chip makers.
Rambus may forfeit royalties on some patents if it loses the government suit and the FTC may try to block the company from collecting as much as $100m a year under agreements the agency said were signed under duress by chip makers such as Samsung, Toshiba and NEC.
Joseph Simons, director of the FTC Bureau of Competition, said: "The conduct at issue here has done substantial harm to important technology markets and threatens to undermine participation in industry standard-setting activities more generally."
The FTC is also trying to stop Rambus collecting cash for its foreign patents against companies that would import chips to the US.
The central allegation against Rambus is that it took part in the Joint Electronic Device Engineering Council for more than four years in the early 1990s without revealing it was working to develop the technology later adopted by the standards board, or that it had a patent for the technology and filed additional patent applications.
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