A semiconductor device includes a semiconductor element, a wiring board including a conductor portion formed on a first surface thereof on which the semiconductor element is mounted, the conductor portion being electrically connected to the semiconductor element, and a concave cap provided to seal the first surface of the wiring board, the concave cap being mounted through an adhesive on the first surface of the wiring boardIn the semiconductor device, a sidewall portion of the concave cap includes an inside surface facing toward the conductor portion of the wiring board, an outside surface positioned on an opposite side to the inside surface, and a bottom surface adhered onto the first surface of the wiring board. The sidewall portion of the concave cap is provided so that a thickness thereof becomes thinner at a portion extending from the outside surface to the bottom surface. Moreover, a dam-shaped member is provided between the conductor portion of the wiring board and the inside surface of the sidewall portion.