PURPOSE: To perform a moisture resistance test in a short time by observing the presence or absence of a corrosion of an aluminum electrode with saline water which contains a large quantity of Cl- and using a sole pellet unit before assembling in a semiconductor device of a finally molding product as a sample.

CONSTITUTION: After a pellet is formed, a final molded product is not manufactured, but the pellet is immediately supplied to a PCT. A vessel 13 for storing saline water w1 is mounted on a net rack 12 of a sealed container 11 in which water W is heated to be set to saturated steam atmosphere of the prescribed temperature and prescribed pressure, and the pellet 1 is dipped in the water w1. If a defect exists in a passivation film of the electrode, the saline water does not pass a gap between a resin mold or the mold and external leads, wirings or heat sink plate, but the defect in contact with the electrode. Thus, the corroding velocity of the electrode formed on the pellet is accelerated as compared with the conventional case.