A semiconductor device includes: a package case in which a semiconductor element is mounted, the package case having a bonding portion; a cap having a bonding portion bonded to the bonding portion of the package case so as to hermetically seal the semiconductor element; and one or more bonding/sealing wires disposed between and in contact with the bonding portion of the package case and the bonding portion of the cap such that the one or more bonding/sealing wires form a closed loop and hermetically seal the semiconductor element.