PURPOSE: To improve the yield and to form a high performance device by employing a normally-off type semiconductor element with a comparatively wider area as a main circuit element conducting a main current and employing a normally-on semiconductor element as an auxiliary element turning off the main element.

CONSTITUTION: An anode of a normally-on type static induction thyristor 2 with a small current capacity connects to an anode A of a normally-off type static induction thyristor 1 with a large current capacity. A cathode of the static induction thyristor 2 connects to a gate G of the static induction thyristor 1. Moreover, a reverse bias power supply 3 connects between a cathode and a gate of the static induction thyristor 2 via a switch 4 being a control switch element. Thus, a main circuit device requiring a large operating area is formed with a normally-off type static induction semiconductor element with high yield and a normally-on type semiconductor element is adopted for an auxiliary device, then the yield is entirely improved.