Effects of gamma-ray irradiation on the electrical characteristics of Al 2 O 3 MOS capacitors such as barrier height, acceptor concentration, series resistance and interface state parameters have been studied by analyzing capacitance-voltage (C-V) and conductance-voltage (G/ x-V) measurements. The fabricated MOS capacitors were irradiated with gamma-rays at doses up to five grays. C-V and G/x-V measurements were recorded prior to and after irradiation at high frequency. The results show that the measured capacitance and conductance values decreased with increasing in irradiation dose and C-V and G/x curves has been shifted toward the negative voltages. Moreover, the series resistance (R s ) and density of interface states increased with increasing in irradiation dose and density of interface states (D it ) were calculated as order of 10 12 eV -1 cm -2 prior to and after irradiation. Due to presence and variations in the R s values, the corrected and the measured C-V and G/x-V exhibited different behaviors. Therefore other electrical characteristics were assessed from corrected C c characteristics. It was observed that acceptor concentration decreased with increasing in barrier height of device due to changes in interface states and diffusion potential.