In order to provide a photothyristor having high breakdown voltage and less-varying light sensitivity by improving the sensitivity and the breakdown voltage of the device while maintaining the device small, the device includes a silicon substrate, a transistor portion including an anode region, a gate region and a cathode region and placed on a first main surface of the silicon substrate, a light-receiving portion for receiving light from the outside, and an electrode for establishing an ohmic contact between the anode region and the cathode region. The light receiving portion includes an oxygen-doped polysilicon film overlaid on the silicon substrate through a transparent insulating film and is disposed to surround the transistor portion. The electrode is placed above the transistor portion and has a double-structure consisting of a center portion and an outer portion surrounding the center portion, and the center portion and the outer portion are electrically connected.