An investigation of spectral hole burning effects is reported in the gain region of InGaAs/AlGaAs strained‐layer single quantum well diode lasers, using a heterodyne nondegenerate pump‐probe technique. This technique permits simultaneous measurement of the femtosecond dynamics and spectral dependence of transient gain in semiconductor lasers. At high bias current, strong spectral hole burning effects were observed. ©1995 American Institute of Physics.