Photo-induced-current transient spectroscopy measurements on CdTe/GaAs strained heterostructures grown by molecular beam epitaxy were carried out to investigate the hydrogenation and the annealing behaviors of the deep levels due to the crystal defects. The six hole-traps of the as-grown CdTe epilayer were observed. As the growth temperature and the rapid thermal annealing (RTA) temperature increased, the intensities of the H5 and the H6 peaks due to the crystal defects decreased, and that of the peak related to the shallow impurities increased. After annealing, the H5 and the H6 deep levels did not disappear in CdTe/GaAs heterostructures. These results indicate that the H5 and the H6 deep levels are related to the crystal defects due to the lattice mismatch. While the H6 signal was remarkably affected by the growth temperature of the CdTe epilayer, it was independent of the thickness of the CdTe. These results indicate that the crystallinity of a CdTe epilayer grown on GaAs(100) is improved by RTA, and that the improvement of the CdTe crystallinity is considered to be due to the elimination of the defects which were formed at heterointerface during the growth of the CdTe epilayer. © 1998 American Institute of Physics.