To prevent a bonding agent from wrapping around the front and the rear surfaces of a wiring board and improve the radiation quality of a semiconductor chip, radiating its generated heat directly to the external, by providing a through-hole in an insulation board for exposing its rear surface to the external, and by providing a dam surrounding the periph ery of the through-hole in the chip mounting region of the wiring board.

In the chip mounting region of one principal surface of a wiring board 1, a through-hole 6 for exposing the rear surface of a semiconductor chip 10 to the external is provided. That is, the semiconductor chip 10 is mounted on the chip mounting region of the front surface of the wiring board 1, interposing a bonding agent 9 between the chip 10 and the board 1, in the state of its rear surface opposed to its principal surface 10a which is exposed to the outside through the through-hole 6. Forming the through-hole 6, e.g. into the shape of a square, the planar size of the through-hole 6 is made smaller than the one of the semiconductor chip 10. Also, in the chip mounting region of one principal surface of the wiring board 1, a dam 7 is so formed between the coat region coated with the bonding agent 9 and the through-hole 6 as to surround the through-hole 6. As a result, the heat radiating quality of the semiconductor chip 10 can be improved, and the bonding agent 9 can be prevented from wrapping around the front and rear surfaces of the wiring board 1.