Metal-oxide-semiconductor (MOS) Schottky diodes were stressed with a bias of 0 V during Co-60-gamma source irradiation with the total dose ranee from 0 to 500 kGy at room temperature. Tin oxide films on Si exhibited a typical behavior of a MOS structure. The variations in the interface state density and series resistance of the Schottky diode have been studied before and after irradiation. The capacitance-voltage (C-V) and conductance-voltage (G/omega-V) characteristics confirm that the interface state density (D-it,) and series resistance (R-s) of the diode are important parameters that strongly influence the electrical parameters of MOS structures before and after irradiation. It has been found that D-it values of MOS structure decreases, while the R, increases with increasing radiation dose. The single-frequency method of Hill-Coleman was used to determine the interface state density. The values, obtained before and after Co-60-gamma source radiation for D-it, are the order of 10(13) eV(-1) cm(-2). (c) 2007 Elsevier B.V. All rights reserved.