Abstract: A fabrication method for a chip size semiconductor package includes the steps of bonding conductive wires on bonding pads formed on an upper surface of a semiconductor chip, putting the semiconductor chip including the bonded conductive wires in an electrolyzer containing an electrolytic solution in such a manner that one end of each of the conductive wires is exposed outside of the electrolytic solution, attaching a plating electrode to an inner wall of the electrolyzer, attaching a conductive plate to serve as a common electrode to the exposed one end of each of the conductive wires; and connecting the conductive plate and the outer wall of the electrolyzer to an electric current source.