The effect of (CO)-C-60 (gamma-ray) irradiation on the electrical properties of Au/SnO2/n-Si (MIS) structures has been investigated using the capacitance-voltage (C-V) and conductance-voltage (G/omega-V) measurements in the frequency range 1kHz to 1MHz at room temperature. The MIS structures were exposed to gamma-rays at a dose rate of 2.12 kGy/h in water and the range of total dose was 0-500 kGy. It was found that the C-V and G/omega-V curves were strongly influenced with both frequency and the presence of the dominant radiation-induced defects, and the series resistance was increased with increasing dose. Also, the radiation-induced threshold voltage shift (Delta V-T) strongly depended on radiation dose and frequency, and the density of interface states N-ss by Hill-Coleman method decreases with increasing radiation dose. (C) 2007 Elsevier Ltd. All rights reserved.