Semiconductor device with heat sink plate

A semiconductor chip is mounted on an upper surface of the heat sink plate that is provided with a plurality of heat releasing terminals on a lower surface of the heat releasing. A plurality of electric signal terminals are regularly disposed in a lattice-like manner around the heat sink plate. Lower end surfaces of the electric signal terminals and the heat releasing terminals are exposed from and sealed with a sealing resin. The heat sink plate is formed as an integrated body including a protruding portion that protrudes from a central portion of an upper surface and supports the semiconductor chip, a plurality of supporting portions that are positioned around a rear surface of the protruding portion so as to support the protruding portion and that are exposed at a rear surface of the sealing resin, the plurality of heat releasing terminals, and a thin-walled portion that is recessed from lower end surfaces of the supporting portions and the heat releasing terminals. Lower surfaces of the protruding portion and the thin-walled portion are covered with the sealing resin. The plurality of supporting portions are disposed so that they are continuous with the protruding portion and symmetrical to each other around the protruding portion. A degree of freedom is improved in board wiring below the heat sink plate in a land grid array type package.