PURPOSE: To improve characteristics and prevent lowering of the yield by polishing an element formation face and removing surface deposits which are produced by gettering.

CONSTITUTION: The double face polishing of a wafer 1 is performed by free abrasive grains and work distortion layers at double faces of the wafer 1 are removed with a mixed acid etching process. Then high temperature treatment is performed in a couple of hours at the high temp. of 1100-1200°C by using a non-oxidizing atmosphere and low temperature treatment is performed in 10-16 hours at the low temp. of 650-700°C and further, intermediate temperature treatment is performed in 16 hours at the temp. of 1000°C and then, a gettering part 1a is formed in the inside of the wafer 1. Deposits 2 are produced on the surface of the wafer 1. Mirror polishing of the wafer 1 is performed by polishing and the deposits 2 are removed completely. This approach improves characteristics and prevents the lowering of the yield.