A silicon wafer for an IGBT is produced by forming an ingot having an interstitial oxygen concentration [Oi] of not more than 7.0.times.10.sup.17 atoms/cm.sup.3 by the Czochralski method; doping phosphorus in the ingot by neutron beam irradiation to the ingot; slicing a wafer from the ingot; performing annealing of the wafer in an oxidizing atmosphere containing at least oxygen at a temperature satisfying a predetermined formula; and forming a polysilicon layer or a strained layer on one side of the wafer.