A semiconductor device according to an embodiment includes: a silicon carbide layer; a silicon oxide layer; and a region disposed between the silicon carbide layer and the silicon oxide layer and having a nitrogen concentration equal to or more than 1×1021 cm−3. A nitrogen concentration distribution in the silicon carbide layer, the silicon oxide layer, and the region have a peak in the region, a nitrogen concentration at a first position 1 nm away from the peak to the side of the silicon oxide layer is equal to or less than 1×1018 cm−3 and a carbon concentration at the first position is equal to or less than 1×1018 cm−3, and a nitrogen concentration at a second position 1 nm away from the peak to the side of the silicon carbide layer is equal to or less than 1×1018 cm−3.