Provided are a semiconductor device wherein heat dissipating characteristics are excellent, reliability is high, and an increase of process cost load is suppressed, and a semiconductor device manufacturing method. A semiconductor device (1) is provided with an insulating substrate (12), semiconductor elements (13, 14), and a cooler (20). The cooler (20) has: a heat dissipating substrate (21) bonded to the insulating substrate (12); a plurality of fins (22) which are provided on the heat dissipating substrate (21) surface on the reverse side of the surface bonded to the insulating substrate (12); and a case (23), which houses the fins (22), and which is provided with an introducing port and a discharge port for a cooling liquid. An end portion of the heat dissipating substrate (21) is disposed in a cutout (23k) that is provided in an upper end portion of a side wall (23b) of the case (23), and the heat dissipating substrate (21) and the case (23) are bonded to each other in a liquid-tight state.