A semiconductor device according to an embodiment includes a semiconductor layer having first and second planes; first and second electrodes; a first semiconductor region of a first conductivity type in the semiconductor layer; a second semiconductor region of a second conductivity type between the first semiconductor region and the first plane; and a third semiconductor region of the second conductivity type surrounding the second semiconductor region. The third semiconductor region includes a first region, a second region, and a third region. A first region, a second region, and a third region are closer to the second semiconductor region in this order. An amount of second-conductivity-type impurities in the first region, the second region, and the third region is less than that of the second semiconductor region. An amount of second-conductivity-type impurities in the second region is higher than that in the first region and the third region.