A semiconductor device according to an embodiment includes a silicon carbide layer, a silicon oxide layer including carbon, the silicon oxide layer including single bonds between carbon atoms which are at least a part of the carbon, the number of the single bonds between carbon atoms being greater than the number of double bonds between carbon atoms which are at least a part of the carbon, and a region provided between the silicon carbide layer and the silicon oxide layer, the region including at least one element from the group consisting of nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), scandium (Sc), yttrium (Y), and lanthanoids (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu).