A semiconductor device, including: a semiconductor chip bonded to a substrate; a heat dissipation base including a fastening portion connected to a heat dissipation portion, the substrate being disposed in a substrate area on the heat dissipation portion, the fastening portion having a fastening hole formed therein; and a case including a protection portion beside an opening area, the protection portion having a fixing hole formed therein corresponding to the fastening hole, the case being disposed on the heat dissipation base so that the substrate is accommodated in the opening area and the protection portion is disposed on the fastening portion. A boundary between the fastening portion and the heat dissipation portion is located outside the opening area of the case in the plan view, and the fastening portion is located lower than the front surface of the heat dissipation portion in a side view of the semiconductor device.