Thermal quenching of photoluminescence from SiGe/Si quantum wells (QWs) grown by low-temperature molecular beam epitaxy is shown to be significantly improved by postgrowth thermal annealing. The dominant mechanism responsible for this improvement is shown to be a reduction of grown-in nonradiative defects, such as vacancy-related complexes. Postgrowth hydrogenation is demonstrated to be less effective as compared to thermal annealing in removing the nonradiative defects. Selective optical excitation has been used to determine the relative contributions of nonradiative recombination channels present in the SiGe QWs and the Si barriers. ©1997 American Institute of Physics.