A semiconductor device includes a structure in which a semiconductor element (chip) is mounted in a cavity formed in a wiring board with an adhesive interposed between the chip and a bottom surface of the cavity, and electrode terminals of the chip are connected via wires to wiring portions formed on the board around the cavity. The chip is mounted in close contact with a side wall of the cavity, the side wall being near a region where a wiring for higher frequency compared with other wirings within the wiring portion is formed. A recessed portion is provided in a region of the bottom surface of the cavity, and a thermal via extending from the bottom surface of the recessed to the outside of the board is provided, the region being near a portion where the chip is in close contact.