Gate turn-off thyristor

Claim 1

A gate turn-off thyristor comprising: a first emitter layer of a first conductivity type which mainly consists of a low impurity concentration region; a first base layer of a second conductivity type formed on said first emitter layer; a second base layer of said first conductivity type formed on said first base layer; a second emitter layer of said second donductivity type formed on said second base layer and divided into a plurality of emitter strips having a nearly rectangular shape, said nearly rectangularly shaped emitter strips being arranged in a circle such that the lengthwise direction of each rectangularly shaped emitter strip coincides with the radial direction of the circle; an anode electrode formed on said first emitter layer; cathode electrodes formed on said emitter strips of said second emitter layer; a gate electrode formed on said second base layer except on portions of said second base layer that form said PN junctions with said emitter strips; and a plurality of high impurity concentration regions of said first conductivity type and of a substantially uniform width formed in said first emitter layer, said high impurity concentration regions being formed such that boundary lines of a projection of said rectangularly shaped emitter strips on said first emitter layer, which boundary lines extend in the lengthwise directions of said emitter strips, are located within at least one of said high impurity concentration regions of said first emitter layer and substantially surround a low impurity concentration region in said first emitter layer that is located just below one of said emitter strips.