In this study, the effect of insulator layer on the electrical characteristics of Au/n-4H SiC diode was investigated. The current-voltage (), capacitance-voltage () and conductance-voltage () measurements were carried out at room temperature condition. Under thermionic emission model, electrical parameters as zero-bias barrier height (), ideality factor (n), interface states (), and series () and shunt () resistances were estimated from forward bias analyses. The values of n and were about 1.305 and 0.796 eV for metal-semiconductor (MS) rectifying diode, and 3.142 and 0.713 eV for metal-insulator-semiconductor (MIS) diode with the insertion of layer, respectively. Since the values of n were greater than the unity, the fabricated diodes showed non-ideal behaviour. The energy distribution profile of of the diodes was calculated by taking into account of the bias dependence of the effective barrier height () and . The obtained values with are almost one order of magnitude lower than those without for two diodes. According to Cheung's model, were calculated and these values were found in increasing behaviour with the contribution of insulator layer. In addition, the plot behaviours with linear dependence between ln() vs. indicated that the dominant conduction mechanism in the reverse bias region was Schottky effect for both MS and MIS diodes. In the room temperature measurements, different from the results of MIS diode, the values of C for MS diode was observed in decreasing behaviour from ideality with crossing the certain forward bias voltage point ( ). The decrease in the negative capacitance corresponds to the increase of G / w.