The metal-oxide-semiconductor (MOS) structures with insulator layer thickness range of 55-430 Angstrom were stressed with a bias of 0 V during Co-60-gamma ray source irradiation with the dose rate of 2.12 kGy/h and the total dose range was 0-5 x 10(5) Gy. The real part of dielectric constant epsilon', dielectric loss epsilon", dielectric loss tangent tandelta and the dc conductivity sigma(dc) were determined from against frequency, applied voltage, dose rate and thickness of insulator layer at room temperature for Au/SnO2/n-Si (MOS) structures from C-V capacitance and G-V conductance measurements in depletion and weak inversion before and after irradiation. The dielectric properties of MOS structures have been found to be strongly influenced by the presence of dominant radiation-induced defects. The frequency, applied voltage, dose rate and thickness dependence of epsilon', epsilon", tandelta and sigma(dc) are studied in the frequency (500 Hz-10 MHz), applied voltage (-10 to 10 V), dose rate (0-500 kGy) and thickness of insulator layer (55-430 Angstrom) range, respectively. In general, dielectric constant epsilon', dielectric loss epsilon" and dielectric loss tangent are found to decrease with increasing the frequency while sigma(dc) is increased. Experimental results shows that the interfacial polarization can be more easily occurred at the lower frequency and/or with the number of density of interface states between Si/SnO2 interfaces, consequently, contribute to the improvement of dielectric properties of Au/SnO2/n-Si (MOS) structures. (C) 2004 Elsevier Ltd. All rights reserved.