SEMICONDUCTOR DEVICE

To suppress a reduction in cooling performance.A cooling chassis (40) has outer lateral faces (40a, 40c) located on the long sides and outer lateral faces (40b, 40d) located on the short sides in plan view. An inlet (40h) communicating with a flow passage area (41) is formed, on the outer lateral face (40b), at a position closer to the outer lateral face (40c). A medium is introduced and flows through the inlet (40h) in the longitudinal direction toward the flow passage area (41). An inflow area (42) is formed, on a flow passage bottom face (41e), at a position closer to the inlet (40h). The inflow area (42) is recessed in a concave shape from the flow passage bottom face (41e), communicates with the inlet (40h), and includes a diffusion face (42d) opposing the inlet (40h).