A semiconductor device includes: a semiconductor chip mounted on a mounting substrate; a first resin filling a gap between the chip and the substrate; a frame-shaped stiffener surrounding the chip; a first adhesive for bonding the stiffener to the substrate; a lid for covering the stiffener and an area surrounded by the stiffener; and a second resin filling a space between the stiffener and the chip. A thermal expansion coefficient of the second resin is smaller than that of the first resin. The first resin includes an underfill part filling a gap between the chip and the substrate and a fillet part extended from the chip region.