General Semiconductor (SEM - Get Report)was down 4% at midday after warning that second-quarter revenue would be down 15% to 17% from the first quarter and earnings per share would be 1 to 3 cents, sharply below the year-earlier 28 cents. The company said demand for its products continues to be weak.

Another chipmaker, United Microelectrionics ( UMC - Get Report), was unchanged after saying it expects a second-quarter operating loss on revenue that will be down 35% from the previous period.

The Philadelphia Stock Exchange Semiconductor Index was up 1.1%.