SEMICONDUCTOR DEVICE

A semiconductor device (1) includes an insulating substrate (14); a semiconductor element (12) carried on the insulating substrate (14); and a cooling device (20) that cools the semiconductor element (12). The cooling device (20) includes a heat radiation substrate (21) joined to the insulating substrate (14); an assembly of a plurality of fins(22) provided on a surface of the heat radiation substrate (21) on a side opposite that of a surface joined to the insulating substrate (14); and a cooling case (23) of a box-like shape that accommodates the fins (22) and has a bottom wall (23a) and side walls (23b). An introducing port (23c) and a discharge port (23d) for a cooling medium are provided in a pair of a first side wall (23b1) and a second side wall (23b2) of the cooling case (23). A diffusion wall causing the cooling medium introduced from the introducing port (23c) to diffuse along the first side wall (23b1) is provided between the first side wall (23b1), in which the introducing port (23c) is provided, and the bottom wall (23a), where the diffusion wall is an ascending inclined surface formed from a bottom side of the first side wall (23b1) toward the bottom wall (23a).