Manufacture of semiconductor products such as LCD driver requires a bump plating step for forming a gold bump electrode having a size of from about 15 to 20 μm. This bump plating step is performed by electroplating with a predetermined plating solution, but projections intermittently appear on the bump electrode during a mass production process. In the invention, abnormal growth of projections over the gold bump electrode is prevented by adding, prior to the gold bump plating step, a step of circulating and stirring a plating solution while erecting a plating cup and efficiently dissolving/discharging a precipitate. This step is performed for each wafer to be treated.