This work presents an attempt related to the charging behaviour of interface states to the nonideal forward bias current-voltage (I-V) and the reverse bias capacitance-voltage (C-V) characteristics of A1-nSi Schottky barrier diodes. The diode showed nonideal I-V behaviour with an ideality factor of 1.50 and was thought to have a metal-interface layer-semiconductor configuration. Considering that the interface states localized at the interfacial layer-semiconductor interface are in equilibrium with the semiconductor, the energy distribution of the interface states was exactly determined from the forward bias I-V characteristics by taking into account the bias dependence of the effective barrier height, Phi(e). The determination of the intercept voltage and interface state density was made by means of a simple interface charge model which has been developed in detail. The I-V characteristics were used for determining the voltage dependence of the barrier height. Although the change in barrier height with applied bias is small, it is important for exactly determining the shape of the interface state density distribution curve. At a frequency of 500 kHz, the nonlinear reverse bias C-2-V plot with the curvature concave downward has been only thought of to be due to the contribution of the capacitance of the interface state charges. It is concluded that the nonlinear nature of C-2-V plots in the frequency range 50-200 kHz has been caused by the interface state charges as well as inversion layer and inversion layer charges. It has been understood by means of the interface state charge model that the C-2-V plots cannot only be interpreted in terms of the contribution of the interface state charges to the device capacitance.