A resin-sealed type semiconductor device has a mount stage, a semiconductor chip mounted on the stage such that a rear surface of the chip is in contact with the stage, a heat spreader associated with the stage and the chip, and a molded resin package encapsulating the stage, chip, and heat spreader. The stage is configured such that the rear surface of the chip is partially covered with the stage, whereby uncovered areas are defined on the rear surface of the electronic component. The heat spreader is complementarily configured with respect to the stage so as to be in direct contact with the uncovered areas of the rear surface of the electronic component, whereby an entire thickness of both the mount stage and the heat spreader is smaller than a total of a thickness of the mount stage and a thickness of the heat spreader.