Abstract: The time‐resolved luminescence spectra from excited conduction subbands in three samples of multi‐quantum‐well GaAs/AlxGa1-xAs (x=0.3 and 1) semiconductors with several well widths and barrier heights were obtained under high‐density excitations by a 30‐ps pulsed laser at 532 nm, which generated electron–hole pairs to the concentration of 1010–1013/cm2 per well per pulse at 77 K. The temperature and the Fermi energy of electron were determined by fitting best the constructed time‐resolved spectrum to the observed, and the time‐dependent electron energy was obtained by using these parameters. The energy‐loss rates of hot electrons are at least twice smaller than the calculated ones induced by the electron‐polar phonon scattering, including the screening effect due to the high carrier density.