PURPOSE: To remove a remaining spontaneous oxide film on a semiconductor wafer by blowing reducing gas or vapor on the surface of the wafer from the specified direction, and keeping the temperature of the wafer within a specified range during the reducing treatment.

CONSTITUTION: Reducing gas or vapor 5 is blown on the surface of a wafer 1 in the perpendicular direction with respect to the surface or in the direction which is inclined from the perpendicular direction by 45°. The temperature of the wafer 1 is kept at 850W1,150°C during the reducing treatment. Therefore, a gas flow without a gas stagnating layer can be formed. New gas which can contribute to the reaction can be always supplied on the surface of the wafer. In this way, the remaining spontaneous oxide film on the semiconductor wafer can be completely removed without defects. The next wafer processing step can be performed effectively, and the characteristics and the like of the device can be improved.