A semiconductor device includes a semiconductor element accommodated in an outer case; a control circuit board fixed to the outer case at a position away from the semiconductor element; and a shield plate provided between the semiconductor element and the control circuit board. The outer case is provided with a support having a convex portion longer than a thickness of the shield plate at a distal end thereof. The shield plate is formed with a through-hole in which the convex portion of the support passes through. The shield plate is fixed to the support with a fixing device engaging with the convex portion.