Deep‐level‐transient spectroscopy on molecular‐beam epitaxially grown square GaAs/ n‐AlxGa1-x As (x=0.24–0.39) single‐quantum wells shows a series of electron traps in the AlGaAs with energies EC-ET at 0.12, 0.22, 0.29, 0.52, and 0.63 eV and with concentrations of about 5×1015 cm-3. The defects are located in the upper AlGaAs layer near the GaAs well layer. The trap concentrations and the widths of the spatial trap distributions (typically 15 nm) are independent of the well width. For all traps, a nonexponential capture process which is logarithmic in time is observed. Time‐dependent depth profiling shows a virtual shift of the trap distribution to the surface for shorter filling pulses. Both effects are due to the nonabrupt depletion edge (Debye tail). No direct emission from the quantum wells is observed.