Memory-chip maker Rambus (RMBS) - Get Report plans to appeal a decision by the Federal Trade Commission Wednesday that determined the company "unlawfully monopolized" technologies, resulting in anticompetitive practices.

The ruling reverses a decision from 2004, when a FTC judge ruled Rambus was not liable.

Shares of Rambus were halted before the announcement. After resumption of trading, the stock was off $3.43, or 20.2%, to $13.55.

The Wall Street Journal Online

reported Wednesday that the FTC found the company distorted a memory-chip standard-setting process for DRAM chips, called JEDEC, and engaged in an anticompetitive "hold-up" of the computer memory industry "through a course of deceptive conduct."

Specifically, the FTC said Rambus was able to conceal its own patents and patent applications until after memory standards were adopted, the

Journal

said. "Only then did Rambus reveal its patents -- through patent infringement lawsuits against JEDEC members who practiced the standard," said the FTC's statement.