Chips are stacked and mounted on a circuit board having external connection electrodes and mounted thereon by wire bonding. At least one of the chips stacked on the chip includes overhung portions each of which has a start point inside bonding pads, is made thinner in a direction towards the outer periphery to an end point reaching the side wall and forms a space used to accommodate ball bonding portions between the overhung portion and the main surface of the chip arranged in the lower stage on a backside corresponding in position to the bonding pads, and insulating members formed to cover the overhung portions and prevent bonding wires of the chip arranged in the lower stage from being brought into contact with the upper-stage chip.