Not only a thermal donor (Si.sub.x O.sub.y cluster) that exists in the state presented immediately after the crystal growth but also a fine oxide precipitate, a point defect cluster or the like can be erased during the process of making a semiconductor wafer. During the slicing process of a semiconductor ingot to the rinsing process after the semiconductor wafer had been polished, preferably, after a damage caused by the lapping work or impurity had been removed by the etching work and before the semiconductor wafer is polished in the final polishing process, the semiconductor wafer is subjected to a heat treatment in a gas ambient containing hydrogen at a temperature higher than 500.degree. C., preferably at a temperature ranging from 900.degree. C. to 1250.degree. so that defects can be decomposed.