A semiconductor device of an embodiment includes a semiconductor layer having a first plane and a second plane, a first semiconductor region of a first conductivity type, a second semiconductor region and a third semiconductor region of a second conductivity type, the first semiconductor region interposed between the third semiconductor region and the second semiconductor region, a first well region of a first conductivity type, a second well region of a first conductivity type separated from the first well region, a first contact region of a first conductivity type, a second contact region of a first conductivity type, a gate electrode provided on the first semiconductor region between the first well region and the second well region, a source electrode having a first region in contact with the first contact region and a second region in contact with the second contact region, and a drain electrode.