Abstract: A groove having a V-shaped section is provided on a bonding surface of an IC chip being as a first small part, while an elongate projection having a V-shaped section to engage with the groove of the first IC chip is provided on a corresponding portion of a bonding surface of an IC chip being as a second small part. Then, the IC chips are bonded together by the action of a holding force resulting from fitting the elongate protection of the second IC chip to the groove of the first IC chip, together with a bonding force produced between the bonding surfaces by interatomic force and metallic bond.