A heatsink plate is to be fixed to a substrate with sufficient strength, so as to prevent the heatsink plate from being stripped off, to thereby secure reliability on the performance of the semiconductor chip. The heatsink plate has both the upper and lower surfaces of the fixing section sandwiched by an adhesive resin. Such structure provides an increased adhesion area between the heatsink plate and the upper surface of the substrate, thereby securing greater fixing strength compared with the conventional structure in which simply the lower surface of the heatsink plate and the upper surface of the substrate are adhered to each other. Accordingly, the heatsink plate can be fixed to the upper surface of substrate with greater strength.