To increase an adhesion strength between a moistureproof board and the main body of a package by burying the moistureproof board inside the main body of the package and forming an uneven section on at least one face of the board.

Between a bottom face of a recessed section 2 which will become a mounting face for a semiconductor element 2 and a bottom face of the main body 1 of a package, a moistureproof board 9 is buried. Due to the existence of the waterproof board 9, the penetration of water from a bottom face of the package through a resin bulk, through which water penetrates the package most easily, can be effectively prevented. The moistureproof board 9 is provided on its both faces with uneven sections 10 and thereby a contact area between the moistureproof board 9 and the main body 1 of the package increases and, at the same time, the adhesion between the moistureproof board 9 and the main body 1 of the package can be also increased due to an anchor effect of the uneven sections 10. By this method, an adhesion strength between the moistureproof board and the main body of the package can be increased without deteriorating the function of the moistureproof board and thereby a semiconductor device with an excellent moistureproof property can be realized.