A semiconductor device according to the present invention includes: a substrate; a heat generating portion provided on the substrate; a cap substrate provided above the substrate so that a hollow portion is provided between the substrate and the cap substrate; and a reflection film provided above the heat generating portion and reflecting a medium wavelength infrared ray. The reflection film reflects the infrared ray radiated to the cap substrate side through the hollow portion due to the temperature increase of the heat generating portion, so that the temperature increase of the cap substrate side can be suppressed. Because of this function, even if mold resin is provided on the cap substrate, increase of the temperature of the mold resin can be suppressed.