PURPOSE: To evaluate quickly and easily the moisture resistance of a resin-sealed semiconductor device by immersing the resin-sealed semiconductor device into a prescribed amt. of soln., extracting contaminant into the soln., measuring the electrostatic capacity value in the extraction liquid and evaluating the moisture resistance.

CONSTITUTION: The resin-sealed semiconductor is inserted together with a prescribed amt. of, for example pure water or soln. of an org. solvent such as alcohol or freon in a clean glass vessel and such resin-sealed semiconductor device is immersed in the soln. in a stage 1 for preparing the extraction liquid of the contaminant. The glass vessel is thereafter hermetically closed and the air is evacuated from the inside of the vessel to maintain a vacuum state in the vessel. The evaporation of the soln. is thereby prevented. Electric discharge is generated at a prescribed temp. for a prescribed period in this state. The prepd. extraction liquid is transferred into another clean vessel and thereafter the electrostatic capacity value of the extraction liquid is measured under prescribed conditions in a stage 2 for measuring electrostatic capacity. The measured electrostatic capacity by the contaminant in the extraction liquid and the preset reference electrostatic capacity value are compared and whether the resin-sealed semiconductor device 1 is accepted or rejected is discriminated in a discrimination stage 3.