Complex changes in the distribution of thermally stimulated current peaks with illumination time and intensity are reported for a sample of semi‐insulating GaAs. With weak illumination for 5 sec, at least six peaks were seen, while after a 1‐min illumination only four peaks were evident. With stronger illumination, the thermally stimulated current essentially consisted of two major peaks, at about 115°K and 278°K. The 115° peak first increased with illumination time, passed through a maximum, and was quite small after a 12‐hr illumination, while the 278° peak became very large.