The gain‐current characteristics of undoped GaInP (660‐nm) bulk lasers have been calculated over a range of temperatures. The calculations use parabolic bands with strictkselection and include band‐gap narrowing and lifetime broadening due to carrier‐carrier interactions at high densities. The broadening lifetime &tgr; has been implemented as a constant value of 10−13s and as a carrier‐dependent value proportional ton−1/3. Using &tgr;=10−13s, our calculations for GaInP at room temperature give a value for the differential gain &bgr; of 0.026 cm−1(A cm−2 &mgr;m−1)−1and a value for the transparency currentJ0of 4.4 kA cm−2 &mgr;m−1. These are in close agreement with experimental results. Results for GaAs at room temperature are also given.