A semiconductor chip (20) including a protruding electrode (bump) (23) in an external extraction electrode is mounted on a wiring board (10), and a semiconductor chip (30) is mounted on the semiconductor chip (20). Electrical connections between a wiring layer (12) of the wiring board (10) and the protruding electrode (23) of the semiconductor chip (20) and between the protruding electrodes of the semiconductor chips (20) and (30) are established by electrolytic plating. Stable connections between the wiring layer (12) and the protruding electrode (23) and between the protruding electrodes of the semiconductor chips (20) and (30) are established by plating films (24) and (33).