The European Patent Office has revoked one of Rambus's European patents on computer memory chip technology, in response to opposition from rival chip makers.
The decision by the EPO's technical board of appeal does not affect the company's other European patents, or its US patents.
The revoked patent related to a technology called "an access time register" and was effective in the UK, Germany, France and Italy.
The EPO has not yet given a reason behind its decision to revoke the patent. That will be revealed when the agency releases its written decision in four to 10 weeks.
Rambus said that although the ruling was a disappointment it is "a small part of a larger picture" and it looked forward to reading the EPO's written decision.
Rambus filed for the European patent in 1991 and opposition was filed against it in 2000 by Micron Europe, Micron Technology Italia and German-based companies Infineon Technologies, Hynix Semiconductor Deutschland and Micron Semiconductor Deutschland. In response, the EPO amended the patent in November of 2002, but that decision was appealed, leading to the decision to revoke the patent.
Rambus has been entangled in a series of US lawsuits involving its patent claims on memory chip technology and faces a decision tomorrow by the US Federal Trade Commission on whether it practised unfair competition by allegedly deceiving a standards-setting body into adopting the memory technology to profit from licensing fees.
Rambus is also involved in a patent suit over memory chip technologies with Infineon which is expected to go to trial in May.
The Infineon spokesman said the company was pleased with the EPO's decision, adding that Rambus has "no basis for all related claims to its patent infringement suit against Infineon".
Asked whether he thought the ruling would affect the US case between the two companies, he said it would be up to the court to decide.
Scarlet Pruitt writes for IDG News Service