Semiconductor stocks are the biggest S&P 500 gainers in Thursday trading, fueled by upbeat commentary from Taiwan Semiconductor Manufacturing Co. on the state of the artificial-intelligence market.

Exact Sciences stock crumbled Thursday on its growing rivalry with Guardant Health and Natera in colon cancer screening.

Shares of Charles River Laboratories (NYSE:CRL) tumbled by 4% as the market reacted to concerns over a potential suspension ...