Gamma-ray irradiation effects on the interface states of Au/SiO2/n-Si (MIS) structures have been determined from capacitance-voltage (C-V) and conductance-voltage (G/omega-V) measurements. The MIS structures were irradiated with gamma-rays at doses up to 100 kGy. The C-V and G/omega-V characteristics were measured at high frequency (1 MHz) and room temperature before and after Co-60 gamma-ray irradiation. The obtained results showed that the barrier height (Phi(b)) decreases with increasing radiation dose, while the interface states (N-ss) and depletion layer width (W-D) increase with the increase in radiation dose obtained from reverse bias C-V measurements. After gamma irradiation, the decrease in capacitance and conductance of MIS structure result in the increase in the semiconductor depletion width. In addition, the voltage dependency of the series resistance (R-s) profile for various radiation doses was obtained from admittance-based measurement method. In addition, the high frequency (1 MHz) capacitance and conductance values measured under both reverse and forward bias have been corrected for the effect of R, to obtain the real capacitance of MIS structure. Experimental results indicate that the total dose radiation hardness of MIS structures may be limited by the decisive properties of the SiO2/Si interface to radiation-induced damage. (C) 2009 Elsevier B.V. All rights reserved.