PURPOSE: To prevent corrosion of sockets and conductors for bias voltge applying in the PCB test to make the humidity-proof property appreciating method of semiconductor devices efficient, by performing the PCB test after performing the PCS test for a prescribed time.

CONSTITUTION: In the PCS test, a semiconductor device is stored in arbitrary vessel 2 and is held in pressure cooker (PC) vessel 3 for a prescribed time. In the PCB test, semiconductor device 1 is held in PC vessel 3 for a prescribed time while applying a bias voltage from bias terminal to semiconductor device 1 through conductor 4. In this PCB test, conductor 4 and the socket are corroded because they are exposed to PC conditions for a long time. However, applying of the bias voltage does not influence corrosion of semiconductor device 1 until water invades from the external to reach the semiconductor chip. Consequently, conductor 4 and the socket are not exposed to the corrodent atmosphere for a long time by performing the PCB test after performing the PCS test for a prescribed time, and thus, the humidity-proof property can be appreciated efficiently.