Patent ID: 7098488

Claim:
An insulated gate bipolar transistor comprising: a semiconductor substrate of a first conduction type; a plurality of trenches on a first principal surface side of the semiconductor substrate; a gate electrode provided in each of a plurality of trenches with an insulator film interposed between; a main well region of a second conduction type on the first principal surface side of the semiconductor substrate, the main well region having a depth that is less than the depth of the trench; a source region of the first conduction type selectively provided on a surface region of the main well region; an emitter electrode electrically connected to both of the source region and the main well region; a sub well region of a second conduction type provided in a region which is other than the main well region and interposed between the trenches on the first principal surface side, the sub well region having a depth that is less than the depth of the trench; a collector layer of the second conduction type formed on a second principal surface side of the semiconductor substrate; a collector electrode electrically connected to me collector layer; and a switching unit provided on the first principal surface of the semiconductor substrate electrically connected and between the sub well region and the emitter electrode, the switching unit isolating the sub well region from the emitter electrode when a forward collector-emitter voltage is low and connecting the sub well region to the emitter electrode when the forward collector-emitter voltage is high.