The Philadelphia Stock Exchange Semiconductor Index, or SOX, was up 15.4% in midafternoon, spiking sharply on the Fed's rate cut.

Sector bellwether

Intel

(INTC) - Get Report

surged and was up 9.1%.

Applied Materials

(AMAT) - Get Report

was up 21.5%.

Other tech indices jumped as well. The

Box Maker Index

was ahead 11.2%.

TheStreet.com Internet Index

was up 15.3%.