In this study, we investigated the electrical properties of Sn/SiOxNy/p-Si metal-insulator layer-semiconductor (MIS) structure. Silicon oxynitride (SiOxNy) thin film was grown on chemically cleaned p-Si substrate by the plasma nitridation process. The chemical composition and surface morphology of the thin film were analyzed using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Electrical measurements of the devices (e.g. current-voltage (I-V ), capacitance-voltage (C-V ), capacitance and conductance-frequency characteristics (C-f and G-f )) were performed at room temperature. The characteristic parameters of the SiOxNy/p-Si interface such as energy position, interface state density and relaxation time constant were obtained from admittance measurements over a wide range of frequencies (from 1 to 500 kHz) for the values of the forward bias between 0.0 V V 1.1 V. The values of the interface state density and their relaxation time constant changed from 3.684 x 10(13) cm(-2) eV(-1) to 3.216 x 10(12) cm(-2)eV(-1) and from 1.770 x 10(-5) s to 6.277 x 10(-7) s, respectively. The obtained values of the interface state density were compared to those of the oxides grown by the other techniques. The experimental results clearly show that the density and location of interface states has a significant effect on electrical characteristics of the MIS structure.