The present invention improves upon the Czochralski method for growing a single-crystal silicon ingot and provides a high quality silicon wafer having an oxide layer with superior voltage-resistance characteristics. An apparatus and method are also provided, whereby vacancy defect density and distribution are uniformly controlled. A single-crystal silicon ingot is grown under a condition where the temperature variation of the ingot is less than or equal to 20.degree. C./cm in the temperature range of 1000 to 1100.degree. C.