A method for heat treatment of a silicon wafer in a reducing atmosphere through use of a rapid thermal annealer (RTA) is provided. In the method, the silicon wafer is heat-treated at a temperature of 1150° C. to 1300° C. for 1 sec to 60 sec in a mixture gas atmosphere of hydrogen and argon. Hydrogen is present in the mixture gas atmosphere in an amount of 10% to 80% by volume. Hydrogen is preferably present in the mixture gas atmosphere in an amount of 20% to 40% by volume. The method decreases COP density on the surface of the silicon wafer to thereby improve electrical characteristics, such as TZDB and TDDB, of the silicon wafer, suppresses the generation of slip dislocation to thereby prevent wafer breakage, and utilizes intrinsic advantages of the RTA, such as improvement in productivity and reduction in hydrogen gas usage.