Semiconductor equipment maker Applied Materials (AMAT.O) is under U.S. criminal investigation for potentially evading export restrictions on China’s top chipmaker SMIC, according to three people familiar with the matter.

The largest U.S. semiconductor equipment maker is being probed by the Justice Department for sending equipment to SMIC via South Korea without export licenses, the sources said. Hundreds of millions of dollars of equipment is involved, one of the people said. Reuters is reporting details of the probe for the first time.

Shares in Applied Materials fell 7.3% after the news and the company reported quarterly results.

The U.S. has restricted shipments of advanced chips and chipmaking equipment to China for national security, and the Justice and Commerce departments launched a task force earlier this year to investigate and prosecute criminal violations of export controls. The rules are aimed at stemming the flow of U.S. technology that could be used to bolster China’s military and intelligence capabilities.