In this work, the investigation of the interface states density and series resistance from capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics in Au/SnO 2 /n-Si (MOS) structures prepared at various SnO 2 layer thicknesses by spray deposition technique have been reported. It is fabricated five samples depending on deposition time. The thicknesses of SnO 2 films obtained from the measurement of the oxide capacitance in the strong accumulation region for MOS Schottky diodes are 37, 79, 274, 401, and 446 A ˚, for D1, D2, D3, D4, and D5 samples, respectively. The C-V and G-V measurements of Au/SnO 2 /n-Si MOS structures are performed in the voltage range from À6 to +10 V and the frequency range from 500 Hz to 10 MHz at room temperature. It is observed that peaks in the forward C-V characteristics appeared because of the series resistance. It has been seen that the value of the series resistance R s of samples D1 (47 O), D2 (64 O), D3 (98 O), D4 (151 O), and D5 (163 O) increases with increasing the oxide layer thickness. The interface state density D it ranges from 2.40 Â 10 13 cm À2 eV À1 for D1 sample to 2.73 Â 10 12 cm À2 eV À1 for D5 sample and increases with increasing the oxide layer thickness.