To prevent useless diffusion of impurities in a silicon wafer as well while a stress in the silicon wafer is relaxed when the impurity-doped silicon wafer is subjected to spike annealing by an RTA method.

A silicon wafer heated up to an annealing temperature is cooled down at a high speed at first and is cooled down finally at a low speed. As the cooling-down speed is low from the middle of cooling-down, a stress in the wafer is relaxed and as the cooling-down is high until the middle of cooling- down, heat energy enough to cut the bonding of impurities of its reduced solubility to the wafer does not work on the impurities and impurities are not uselessly diffused in the wafer as the bonding of the impurities to the wafer is not cut.