A semiconductor device includes an insulator substrate mounted on a base plate, the insulator substrate having an upper electrode, semiconductor chips mounted on the insulator substrate, external terminals for establishing external electrical connections of the semiconductor device, wires for establishing electrical connections among the external terminals, the upper electrode and the semiconductor chips, a case accommodating the insulator substrate, the semiconductor chips, the external terminals and the wires which are sealed by a sealing material filled in the case, a lid for protecting an upper part of the sealing material, and an insulative low electrification covering fitted on each wire, the low electrification covering having a lesser tendency to produce an electric charge buildup than the sealing material.