The admittance spectra of Au/Pd/Ti-SiO2-(n) GaAs structures have been recorded at different gate voltages (between 0 and 30 V) and at different temperatures (between 30 and 92 degreesC). The complex behaviour indicating the existence of a broad spectrum of the time constants have been noted. We have described these characteristics by an equivalent circuit consisting of two parallel branches including the constant phase elements (CPE1 and CPE2) in series with resistors in parallel with the space charge layer capacitance, all of which is in series with an insulator capacitance and series resistance. The parameters of that circuit have been estimated and characteristic time constants have been calculated at different temperatures. From the Arrhenius plots analysis the capture cross-section and activation energy of states influencing the frequency response of the investigated system have been determined. The contribution of the electron processes evoked by SiO2-GaAs interface states and the bulk traps in GaAs has been established. They are represented by CPE1 (with the parameter n(1) similar to 0.51) and by CPE2 (with the parameter n(2) - 0.89-0.95), respectively, connected in series with resistances. The tunneling of the electrons between semiconductor and spatially distributed interface states has been supposed as the origin of CPEL1. (C) 2004 Elsevier B.V. All rights reserved.