The US International Trade Commission (USITC) has launched four investigations involving the import of computers or electronic device components, including one based on a complaint that several companies are violating patents on DRAM chips.

The USITC also voted to launch an investigation, based on a complaint by IBM, into the import of motherboards, graphics cards, notebook computers, server computers, barebones computers and routers by Asustek Computer of Taiwan and Asus Computer International of Fremont, California.

In the DRAM (dynamic RAM) case, Tessera of San Jose, California, filed a complaint on 7 December alleging that 18 companies violated its patents for semiconductor chips with a minimized chip package size. Acer and Kingston Technology are among the companies named in Tessera's complaint.

The commission on Friday also announced it has initiated so-called 337 investigations into the import of silicon microphone packages used in mobile phones and semiconductor lasers used in disc drives.

In the Tessera complaint, the company accused competitors of violating four semiconductor patents. The company has filed a lawsuit in the US District Court for the Eastern District of Texas, as well as the USITC complaint. The US Patent and Trademark Office has granted re-examination requests on two of those patents.

Representatives of Acer and Kingston didn't immediately respond to a request for comments on the USITC investigation.

IBM filed a complaint on 5 December, asking the USITC to bar Asustek and North American subsidiary Asus Computer International from importing equipment using PC power supplies, cooling fans and clustering technologies into the US. IBM accused Asustek of infringing three patents related to those technologies.

IBM attempted to reach a licensing agreement with Asustek after a licensing deal expired in December 2004, an IBM spokesman said in December. An Asus spokeswoman didn't immediately respond to a request for comments.

The semiconductor laser complaint covers lasers used in high-definition disc drives. The investigation is based on a complaint filed by Seoul Semiconductor of Korea on 4 December, alleging that Nichhia of Japan has violated its patent.

In the silicon microphone case, the patented technology covers microphones in several devices, including mobile phones. The complaint, filed by Knowles Electronics of Itasca, Illinois, on 6 December, alleges that Mems Technology Berhad of Malaysia has violated its patents.

The cases will be referred to an administrative law judge, who will schedule and hold a hearing. The judge will make an initial determination as to whether there is a violation of Section 337 of the US Tariff Act of 1930. That initial determination is subject to review by the USITC.

Within 45 days, the commission will set a target date for completing the investigations.