Results are presented of admittance spectroscopy measurements on the lattice‐matched In0.52Al0.48As/In0.53Ga0.47As single‐quantum‐well structures. It has been found that the perpendicular conductivity of the structure is controlled by the strong temperature dependence of the space‐charge region width around the quantum‐well layer. This process is governed by a high density of deep electron traps present in the layers adjacent to the quantum well. Therefore, the energy activation of perpendicular conductivity is determined by the deep‐level defects rather than the thermionic emission of electrons from the quantum well. Because of this, it is impossible to extract the magnitude of the band offset between the quantum well and barrier layers from the admittance measurements performed in this study. ©1995 American Institute of Physics.