not only a thermal donor 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 ° c ., preferably at a temperature ranging from 900 ° c . to 1250 ° so that defects can be decomposed .