Patent ID: 7307330

Claim:
A reverse blocking semiconductor device comprising: a drift layer of a first conductivity type; a MOS gate structure including a base layer of a second conductivity type selectively formed in a front surface region of the drift layer, an emitter region of the first conductivity type selectively formed in a surface region of the base layer, a gate insulation film covering a surface area of the base layer between the emitter region and the drift layer, and a gate electrode deposited on the gate insulation film; an emitter electrode in contact with both the emitter region and the base layer of the MOS gate structure; an isolation region of the second conductivity type surrounding the MOS gate structure through the drift layer and extending across the entire thickness of the drift layer; a collector layer of the second conductivity type formed on a rear surface of the drift layer and connecting to a rear side of the isolation region; a collector electrode in contact with the collector layer; a plurality of field limit layers of the second conductivity type in the front surface region of the drift layer between the emitter electrode and the isolation region, each of the field limit layers having a ring shape; and a plurality of field limit electrodes, each in contact with each of the field limit layers, each of the field limit electrodes having a ring shape, and being at a floating electric potential; wherein a plurality of the field limit electrodes exist in the side of the emitter electrode and each of the field limit electrodes in the side of the emitter electrode has a larger outward extension portion than an inward extension portion; and a plurality of the field limit electrodes exist in the side of the isolation region and each of the field limit electrodes in the side of the isolation region has a larger inward extension portion than an outward extension portion.