The results of experimental studies of the subpicosecond relaxation dynamics of photoexcited charge carriers in an In0.22Ga0.78As/GaAs quantum-well heterostructure are reported. From photoluminescence studies of the structure by the upconversion technique, the cooling rate of charge carriers in the quantum well and the time of charge-carrier trapping into the well are estimated to be similar to 1 ps at 300 K and at similar to 6.5 ps at 10 K.