SEMICONDUCTOR DEVICE

PROBLEM TO BE SOLVED: To provide a semiconductor device capable of effectively reducing on-state resistance and output capacitance without reducing breakdown voltage between a source and a drain, and to provide a photo relay comprising the semiconductor device. SOLUTION: A semiconductor device 100 comprises a semiconductor substrate 110; a semiconductor layer 120 provided on the front surface of the semiconductor substrate; a base layer 130 provided on the front surface of the semiconductor layer 120; a source layer 140 provided on the front surface of the base layer; a trench 150 formed such that it penetrates from the front surface of the source layer through the source layer, the base layer, and the semiconductor layer and reaches the semiconductor substrate; a gate electrode 170 extending from the source layer to at least the semiconductor layer in the trench; and an insulator 160 provided between the gate electrode and the base layer, such that the interior of the trench under the gate electrode is filled with the insulator and the gate electrode is insulated from the base layer. COPYRIGHT: (C)2006,JPO&NCIPI