We present a theoretical prediction of the threshold current density and the temperature sensitivity of a GaN laser operating in the intrinsic band‐to‐band transition. We calculate the material gain and spontaneous emission spectrum for unintentionally doped bulk GaN under carrier injection. All stimulated and spontaneous emission calculations are compared to those of bulk GaAs. The transparency carrier density of GaN is found to be more than four times that of GaAs, and the momentum matrix element for optical transitions in bulk GaN is estimated to be about one‐third the value in GaAs. In addition, the differential gain is approximately four times smaller in GaN. These differences are attributed to the larger effective masses of the electrons and holes in GaN. The calculated characteristic temperatureT0of the threshold current density for a GaN laser ranges from 185 to 220 K, which agrees well with the recently observed data from optical pumping experiments. ©1995 American Institute of Physics.