We report the first investigation of the frequency dependent effects of gamma irradiation on interface state density and series resistance determined from capacitance voltage (C-V) and conductance-voltage (G-V) characteristics in SnO2/n-Si structures prepared by spray deposition method. The samples were irradiated using a Co-60 gamma-ray source at 500 kGy at room temperature. The C-V and G-V measurements of the samples were performed in the voltage range -6V to 2 V and at 10 kHz, 100 kHz, 500 kHz and 1 MHz at room temperature before and after 500 kGy irradiation. The measurement capacitance and conductance are corrected for series resistance. It has been seen that the value of the series resistance R, of sample decreases from 204 Omega to 55.4 Omega with increasing the frequency before irradiation while it decreases from 248 Omega to 60 Omega with increasing frequency at 500 kGy irradiation. It has been found that and D-it values of MOS structure increases up to 100 kHz and then decreases up to I MHz while the R-s increases with increasing irradiation dose for our sample. The interface state density Dit ranges from 1.83 x 10(13) cm(-2) eV(-1) for before irradiation to 1.54 x 10(13) cm(-2) eV(-1) for 500 kGy irradiation dose at 500 kHz and decreases with increasing frequency. (c) 2007 Flsevier B.V. All rights reserved.