THYRISTOR

PURPOSE:To enable an element to turn on stably even in case of refiring, by eliminating a part of a secondary emitter and a secondary base and by thinning the secondary base locally. CONSTITUTION:A preliminary thyristor 20 is formed at a section of a P-base 4 of which thickness is reduced locally by etching, etc. A preliminary cathode electrode 23 is formed so that a bottom of the P-base 4 having a locally reduced thickness may be shorted to the primary thyristor 20. The preliminary cathode electrode 23 is constructed not to come into contact with a cathode electrode 7. Since the P-base 4 of the preliminary thyristor 20 is thin, firing sensitivity of the thyristor 20 is high in comparison with the cathode 7 of a main thyristor 1. Therefore, if misfiring is made at an unspecified position in the thyristor 1, the nearby preliminary thyristor 20 fires first. In this way, even if the thyristor body 1 misfires when forward voltage is applied again during turn-off, safe turn-off is ensured.