We have examined carrier thermalization, recombination, and band filling in GaAs/AlGaAs quantum boxes with low-temperature cathodoluminescence (CL). The temperature dependence of the quantum box CL intensity forT⩽90 K exhibits an Arrhenius behavior, as a result of carrier thermalization between the quantum box and surrounding barrier regions. The width of the quantum box luminescence is found to increase rapidly with an increasing excitation density and reveals an enhanced phase-space and real-space filling, in comparison to the behavior observed for quantum wells. ©1997 American Institute of Physics.