A semiconductor device which has a preferable construction for downsizing, in which chip part(s) and a cap are not short-circuited, is provided. The semiconductor device includes: a substrate having a first surface with a cavity and a second surface opposite to the first surface; a semiconductor chip arranged in the cavity; a chip part mounted on the second surface of the substrate; a heat sink which is mounted on the second surface of the substrate and transfers heat liberated from the chip; a cap which is fitted to the substrate, covers the second surface of the substrate, and is joined to the heat sink; and an insulator provided between the cap and the chip part. By providing the insulator, short-circuiting of the chip part and the cap is prevented. Consequently, a distance between the cap and chip part can be shortened to downsize the size of semiconductor device.