The companies said the decision comes after the Department of Justice advised them that it would not continue with a consent decree that they had been negotiating.
The stocks were halted for news pending around 5:55 p.m. ET and resumed trading around 6:30 p.m. ET.
Shares of Lam Research fell more than 2 percent in extended trading, while KLA-Tencor shares fell nearly 5 percent.