The Japanese suit was filed in the Tokyo District Court against Hynix Semiconductor Japan and alleges that Hynix violated three of Toshiba's patents, covering NAND-type flash memory chips.

The suit seeks monetary damages and a halt to sales of the Hynix products that Toshiba alleges infringe upon its patents.

Toshiba also filed a broader suit against Hynix and some of its US subsidiaries in the US District Court for the Northern District of Texas.

That suit alleges Hynix has infringed upon four patents on NAND-type flash memory and three relating to DRAM. Like the Japanese suit, it asks for an injunction against sale of the products and monetary damages.

Both lawsuits relate to a patent cross-licensing agreement signed between Toshiba and Hynix in August 1996.

The agreement expired on December 31, 2002, and, despite negotiations, the two companies have been unable to agree on a revision of the arrangement, Toshiba says. Hynix could not be immediately reached for comment.

"Toshiba wants money ... and it wants to protect its technology," says Kim Soo-Kyoum, program director for semiconductor research at IDC.

Kim says that the suits filed by Toshiba are in support of legal moves made in mid-October by its flash memory development and production partner, SanDisk, against STMicroelectronics NV, which partners Hynix in making flash chips.

On October 18, SanDisk filed a complaint with the US International Trade Commission alleging that NAND-type flash memory chips made by STMicroelectronics NV infringed a SanDisk patent.

SanDisk requested that STMicroelectronics' NAND flash memory chips be barred from sale in the US. SanDisk also filed suit in the US District Court for the Northern District of California, involving the same patent, and sought an order declaring that its products did not infringe 14 US patents assigned to STMicroelectronics.

Flash memory has the ability to maintain its contents even after power to the chip has been turned off.

This has made it one of the most commonly used types of memory chip in devices such as consumer electronics products, cellular telephones and digital music players. DRAM is the most commonly used type of memory in PCs.

Toshiba is the world's second biggest NAND flash memory maker, with about 34% market share, according to IDC. Meanwhile, Hynix, which has started volume production of NAND flash recently, has only a very small share, according to Kim.

However, if Toshiba forces Hynix to pay royalties through successfully prosecuting the patent dispute, Toshiba will benefit from any success that Hynix and STMicroelectronics have in the market. "It is a win-win situation for Toshiba," Kim says.

The total NAND flash memory market is expected to be $6,8bn in 2004 and will grow to a value of $8,2bn in 2008, according to IDC estimates.

Another reason for Toshiba to file its actions is concern that increasing flash memory production by Hynix and STMicroelectronics may further erode prices that are already falling, cutting into Toshiba's and SanDisk's profits, according to an industry insider.

Toshiba was the fourth largest manufacturer of flash memory in 2003, according to data from market research company IDC. Toshiba had a 13,3% share of the global $10,7bn market on a revenue basis, behind Samsung Electronics, Fujitsu AMD Semiconductor and Intel, according to IDC's estimates.

Hynix was not ranked in the top ten. However, in the DRAM market, Hynix was the Number 2 producer of chips in the second quarter of this year, according to IDC figures. The company had a 16,1% share of the $7bn global market behind market leader Samsung Electronics.