Abstract Effect of annealing at (720-1000) K/1400 K under argon pressure up to 1.2×109 Pa on photoluminescence related to defects created in oxygen-containing (Czochralski grown or oxygen-implanted) silicon was investigated by optical, synchrotron, X-ray and related methods. For the samples pressure-treated at 1400 K the intensity of dislocation-related photoluminescence lines was found to be reduced in comparison to that for the samples annealed at ambient pressure. An increase of photoluminescence intensity at 0.97–1.04 eV, a reduction of X-ray diffuse scattering intensity as well as creation of large (up to 15 μm) oxygen-related defects were stated for the samples annealed at 1400 K under high pressure. An explanation of observed phenomena is proposed.