Micron, the US's biggest maker of memory chips, has said it is being investigated for anti-competitive practices by the US Justice Department.

Micron said it has been served with a grand jury subpoena as part of an industry-wide inquiry. The firm denies any wrong-doing.

"We're cooperating with the (Justice) department," said Micron spokesman Sean Mahoney. "It's an industry-wide investigation and we're cooperating."

Micron is the biggest US manufacturer of dynamic random access memory, or DRAM, chips which are used in PCs and a host of other consumer electronic goods.

Markets take fright

"Micron does not believe it has violated U.S. antitrust laws," said Kipp Bedard, vice-president of corporate affairs.

"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," Mr Bedard added.

Combined with profits warnings from two other big US technology firms, the news sent stock markets plunging across Asia from Australia to Singapore.

And there was more bad news for the tech sector, when shares in technology company Rambus lost more than 20% on Wednesday after the US Federal Trade Commission said it had filed an anti-trust complaint against it.

The agency claimed that Rambus took part in an industry standard-setting body for more than four years, without revealing that it had several patents for technology ultimately adopted by the group.

Struggling industry

Chip makers worldwide have cut jobs and capacity during the last 12 months to cope with tough market conditions.

Mr Mahoney said Micron could not comment on which other companies might be part of the Justice Department's inquiry.

The firm had been issued with a grand jury subpoena from the US District Court for the Northern District of California.

Micron's shares have suffered in tandem with other technology stocks, shedding 38% of their value in the last 12 months.

Last month, Micron ditched plans to buy a slice of Korean chip giant Hynix after months of talks failed to produce a deal.