We report the dependence on the excitation power and temperature of the photoluminescence emission from a quaternary Ga0.75In0.25As0.04Sb0.96/Al0.22Ga0.78As02Sb0.98strained multiple‐ quantum‐well structure grown by molecular‐beam epitaxy. Sharp exciton resonances are observed up to room temperature and have been attributed to localized excitons for temperatures ≤80–100 K and to free excitons at higher temperatures up to room temperature by a comparative study with temperature‐dependent absorption spectroscopy. We conclude that the dominant luminescence quenching mechanism in this quaternary system is mainly due to the trapped excitons thermalizing from the localized regions below 100 K, and the thermal carrier activation from the first electron and heavy‐hole subbands to the second electron and heavy‐hole subbands at higher temperatures. ©1995 American Institute of Physics.