In this work, the investigation of the interface state density and series resistance from capacitance-voltage (C-V) and conductance-voltage (G/oÀV) characteristics in In/SiO 2 /p-Si metal-insulator-semiconductor (MIS) structures with thin interfacial insulator layer have been reported. The thickness of SiO 2 film obtained from the measurement of the oxide capacitance corrected for series resistance in the strong accumulation region is 220 A ˚. The forward and reverse bias C-V and G/oÀV characteristics of MIS structures have been studied at the frequency range 30 kHz-1 MHz at room temperature. The frequency dispersion in capacitance and conductance can be interpreted in terms of the series resistance (R s ) and interface state density (D it ) values. Both the series resistance R s and density of interface states D it are strongly frequency-dependent and decrease with increasing frequency. The distribution profile of R s -V gives a peak at low frequencies in the depletion region and disappears with increasing frequency. Experimental results show that the interfacial polarization contributes to the improvement of the dielectric properties of In/SiO 2 /p-Si MIS structures. The interface state density value of In/SiO 2 /p-Si MIS diode calculated at strong accumulation region is 1.11 Â 10 12 eV À1 cm À2 at 1 MHz. It is found that the calculated value of D it (E10 12 eV À1 cm À2 ) is not high enough to pin the Fermi level of the Si substrate disrupting the device operation.