Patent ID: 7405435

Claim:
A semiconductor device comprising: a thyristor having an anode connected to a first terminal and a cathode connected to a second terminal, the thyristor including a first bipolar transistor of a first polarity having an emitter connected to the first terminal, and a second bipolar transistor of a second polarity having a collector connected to a base of the first bipolar transistor, a base connected to the collector of the first bipolar transistor, and an emitter connected to the second terminal, a trigger circuit configured to fire the thyristor when surge voltage is applied to the first terminal, the trigger circuit including a plurality of diodes in which cathodes and anodes are sequentially connected in series between the first terminal and the base of the second bipolar transistor, and a surge detection/leakage reduction circuit provided between the base of the second bipolar transistor which acts as a gate of the thyristor and the second terminal, and configured to interrupt current flowing from the trigger circuit to the second terminal in normal operation mode and set trigger voltage which is used to fire the thyristor in cooperation with the trigger circuit at surge voltage application time, wherein the surge detection/leakage reduction circuit includes a MOS transistor of a first conductivity type having a current path connected at one end to a node, which is directly connected to both to one end of the plurality of diodes sequentially connected in series and the base of the second bipolar transistor, and connected at the other end to the second terminal, as well as a gate connected to the base of the second bipolar transistor.