The Fair Trade Commission said yesterday its three-year investigation into anti-trust charges involving four NAND flash memory chipmakers has found no evidence of violations.

The watchdog began its probe in January 2007 to find whether the four NAND flash memory chipmakers -- two Korean companies, one Japanese firm and one U.S. firm -- have colluded to fix chip prices and output, and affected the local memory chip market.

It found that the four companies had not committed any wrongdoing and that the FTC closed the case.

The commission did not name the four companies, but industry officials noted that major suppliers of NAND memory chips for the Korean market include Samsung Electronics, Hynix Semiconductor and Toshiba of Japan. The biggest U.S. suppliers include SanDisk, Micron and Intel.

"Overseas anti-trust agencies also looked into the case, but they also are said to have closed the probe recently," the FTC said in a statement.

In August, news reports said the U.S. Justice department concluded a two-year price-fixing investigation of the flash memory industry with no further action being taken.

"With the closure of the flash memory case, the FTC has finished cartel investigations into cases involving all memory chips, including DRAMs and SRAMs," the FTC said.

NAND flash memory chips are used to store music and photos in portable digital gadgets such as MP3 players, flash cards, USB memories and digital cameras.

Samsung Electronics is the No. 1 NAND flash memory chipmaker with 42.1 percent of the global market share as of 2006, followed by Toshiba with 19.6 percent, Hynix 17.3 percent and SanDisk, 11.3 percent, according to data by market research firm Gartner and Dataquest.

The price of a 4-giga NAND flash memory chip has declined more than 50 percent annually to $16.4 in 2007 from $333.6 in 2003 due to a severe supply glut, according to Dataquest.