We have demonstrated continuous wave operation of 2.7‐&mgr;m InGaAsSb/AlGaAsSb multiquantum‐well diode lasers up to a temperature of 234 K (−39 °C). These devices were grown by molecular‐beam‐epitaxy. They have a tendency to operate in a dominant single mode over well‐defined temperature and current intervals. A comparison of spontaneous emission spectra shows that above threshold, the quasi‐Fermi level is pinned and that most of the carriers are injected into nonlasing states. This effect leads to a rapid decrease of differential efficiency with increasing temperature. ©1995 American Institute of Physics.