A transistor comprises: an insulating layer; a semiconductor layer provided on a major surface of the insulating layer; a gate insulating layer provided on the base region; and a gate electrode provided on the gate insulating layer. The semiconductor layer has a source portion having a plurality of source regions of a first conductivity type and a plurality of base contact regions of a second conductivity type, the source regions being alternated with the base contact regions, a drain portion of the first conductivity type, and a base region of the second conductivity type provided between the source portion and the drain portion, the base region being in contact with the source regions and the base contact regions. A junction between the source regions and the base region is closer to the drain portion side than a junction between the base contact regions and the base region.