A semiconductor device having first through third layers. The first layer has a first conductivity type. The second layer has a second conductivity type different from the first conductivity type. The third layer has a first portion having the second conductivity type and a second portion having the first conductivity type. A trench structure is located in the first portion and is completely surrounded by the first portion in an area extending from a first surface of the third layer to a second surface of the third layer.