A semiconductor device includes a wiring board that includes a first insulating layer, a first conductive layer arranged over the first insulating layer, a second conductive layer arranged under the first insulating layer, the wiring board further including a magnetic layer that is arranged between the first insulating layer and the first or second conductive layer and that has a higher specific magnetic permeability than the first and second conductive layers, and a carbon layer that is arranged between the first insulating layer and the first or second conductive layer and that has a higher thermal conductivity in a planary direction than the first and second conductive layers; a semiconductor chip electrically connected to the first and second conductive layers; and an insulating circuit board arranged separately from the wiring board and that has the semiconductor chip mounted thereon.