A semiconductor device has a conductive interconnection layer formed on a semiconductor substrate covered with a protection insulation film. A pad electrode opening is provided in the protection insulation film so that the surface of the conductive interconnection layer is exposed in the region which becomes the pad electrode. The conductive interconnection layer is electrically connected to an external terminal by a bonding wire. At least the surface of the protection insulation film in the proximity of the pad electrode opening and the inner peripheral side face of the pad electrode opening are covered with an elastic insulation film. The pad electrode opening is covered with the bonding wire. Since the conductive interconnection layer is not exposed at the pad electrode opening according to this structure, the phenomenon of moisture intruding into the pad electrode opening to corrode the conductive interconnection layer is prevented to improve reliability. The semiconductor device of this structure is formed by covering the inner surface and its proximity of the pad electrode opening with an elastic insulation film, forming an opening in the elastic insulation film at the bottom of the pad electrode opening, and connecting the pad electrode to an external terminal by wire bonding.