A semiconductor device comprises a semiconductor substrate comprised of an interposer having one surface and a semiconductor element provided on the one surface of the interposer, the semiconductor element including a light receiving portion for receiving light thereon; a transparent substrate having light-transmitting property and one surface facing the light receiving portion, the transparent substrate arranged in a spaced-apart relationship with the one surface of the interposer through a gap formed between the one surface of the interposer and the one surface of the transparent substrate; and a spacer formed in a shape of a frame, the spacer positioned between the one surface of the interposer and the one surface of the transparent substrate for regulating the gap, and the spacer having an inner surface and an outer surface, wherein the one surface of the interposer, the one surface of the transparent substrate and the inner surface of the spacer form a space which is hermetically sealed, and wherein the spacer has a wall including at least one thin wall portion and a thick wall portion other than the at least one thin wall portion, and a vapor permeability of the at least one thin wall portion is greater than a vapor permeability of the thick wall portion, wherein a vapor allowed to flow into the space through the wall of the spacer from an outside preferentially permeates from the space to the outside through the thin wall portion.