According to an embodiment, a semiconductor device includes a first electrode, a second electrode, a first semiconductor region, a plurality of second semiconductor regions, a plurality of third semiconductor regions, a plurality of third electrodes, and a plurality of gate electrodes. The gate electrodes and the third electrodes are arranged parallel in a second direction and periodically with a third arrangement cycle such that the ratio of the number of the gate electrodes and the third electrodes in the first region is m3 to m4 (m3, m4 being positive integers and m3 being more than or equal to m4).