The charge storage effect in layered dielectrics was investigated using Al-Al2O3-SiO2-Si (MAOS) capacitor structures, prepared by pyrolytic deposition of γ-Al2O3 on thermally oxidized silicon. The thickness of the underlying SiO2 (tSiO 2 ) in these structures was chosen such that the storage characteristics could be monitored by the capacitance-voltage technique in two conduction regimes. In the regime (t SiO 2 > 50Å) where charge accumulation at (or removal from) the Al2O3-SiO2 interface is due to the conductivity difference between the dielectric layers, the switching characteristics of the MAOS devices subjected to long dc pulses exhibit decreasing reversibility with decreasing tSiO 2. In the direct tunneling regime (tSiO 2 < 35Å), application of positive or negative pulses of μsec duration to the devices results in a unidrectional flatband-voltage shift to increasingly higher positive values. A tentative model of multilevel trapping will be presented to explain these experimental observations. © 1971 The Metallurgical Society of American Institute of Mining.