A semiconductor device includes a wiring board that has a conductive pattern formed on at least one principal surface, and an IC chip that is mounted on the wiring board. The IC chip includes a plurality of electrodes to make conductor connection with the wiring board. The conductive pattern includes a lead line pattern and a heat dissipation pattern. The lead line pattern is connected with at least one of the plurality of electrodes through a conductor. The heat dissipation pattern is physically spaced from the IC chip and the lead line pattern and has a larger surface area than the lead line pattern. Further, the lead line pattern and the heat dissipation pattern are placed opposite to each other with a gap therebetween, and their opposite parts respectively have interdigitated shapes and are arranged with the respective interdigitated shapes engaging with each other with the gap therebetween.