CMC Magnetics (TPE:2323) sold about 4.6 million shares of YMTC for a total of NT$353.6 million.
The shares were sold between March 27 and May 22, at an average price of NT$76.76 per share.
The sale generated a gain of NT$9.2 million, according to a Thursday Taiwan Exchange filing.
After the disposal, CMC Magnetics holds 152,000 shares of YMTC, representing 0.004% of the total shares, the optical storage products manufacturer said.