PURPOSE: To obtain low loss and good turn-OFF characteristics by forming an n-buffer of constant thickness between an n--base layer and an anode diffusion layer and by making the thickness of the base layer thin until the tip of a depletion layer at the time of turn-OFF can reach the n-buffer layer.

CONSTITUTION: A normally-OFF type electrostatic induction type thyristor comprises an anode diffusion layer 3 of a player, a gate diffusion layer 5 and a cathode diffusion layer 4 of an n--layer formed via an n--base layer 2 of predetermined thickness and further a depletion layer 6 formed on the base layer 2 around a periphery of the gate diffusion layer 5 and the cathode diffusion layer 4. Then a buffer layer 1 of constant thickness is formed between the base layer 2 and the anode diffusion layer 3, while thickness of the base layer 2 is made thin until the tip of the depletion layer 6 at the time of turn- OFF can reach the buffer layer 1. Thus the base region can be thin, channel closure can be attained by the highly resistant depletion layer, breakdown strength can be high, and switching loss can be reduced.