A semiconductor device includes a plurality of leads, a semiconductor element electrically connected to the leads and supported by one of the leads, and a sealing resin covering the semiconductor element and a part of each lead. The sealing resin includes a first edge, a second edge perpendicular to the first edge, and a center line parallel to the first edge. The reverse surfaces of the respective leads include parts exposed from the sealing resin, and the exposed parts include an outer reverse-surface mount portion and an inner reverse-surface mount portion that are disposed along the second edge of the sealing resin. The inner reverse-surface mount portion is closer to the center line of the sealing resin than is the outer reverse-surface mount portion. The outer reverse-surface mount portion is greater in area than the inner reverse-surface mount portion.