A semiconductor device including a semiconductor substrate having oppositely facing first and second surfaces, the first surface being an active surface and provided with an electronic element thereon, a pad electrode to be connected to the electronic element in a peripheral portion of the electronic element on the active surface, a first opening extending from the second surface toward the pad electrode so as not to reach the first surface of the semiconductor substrate, a second opening formed to reach the pad electrode from a bottom surface of the first opening and having a diameter smaller than that of the first opening, an insulating layer formed to cover sidewall surfaces of the first opening and the second opening, and a conductive layer formed, inside of the insulating layer, to cover at least an inner wall surface of the insulating layer and a bottom surface of the second opening.