Visible luminescence from thermal treated intrinsic Czochralski‐grown silicon is reported. Oxygen precipitates were formed in a nearly oversaturated silicon by a two‐step thermal treatment with auxiliary use of high pressures. A wide photoluminescence band peaked at about 2.3 eV is observed in those samples for which the first treatment was performed at a relatively high temperature and which show a higher amount of oxygen precipitates and oxygen related defects. Scanning electron microscopy of the best performing samples show the presence of submicron conglomerates on the surface. We have tentatively attributed the luminescence emission to the defects in the suboxide SiOxphase formed in the oxygen precipitates. ©1996 American Institute of Physics.