In this study, the effect of Si 3 N 4 insulator layer on the electrical characteristics of Au/n-4H SiC diode was investigated. The current-voltage (I −V), capacitance-voltage (C−V) and conductance-voltage (G/w−V) measurements were carried out at room temperature condition. Under thermionic emission model, electrical parameters as zero-bias barrier height (Bo), ideality factor (n), interface states (D it), and series (R s) and shunt (R sh) resistances were estimated from forward bias I −V analyses. The values of n and Bo 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 Si 3 N 4 layer, respectively. Since the values of n were greater than the unity, the fabricated diodes showed non-ideal I −V behaviour. The energy distribution profile of D it of the diodes was calculated by taking into account of the bias dependence of the effective barrier height (e) and R s. The obtained D it values with R s are almost one order of magnitude lower than those without R s for two diodes. According to Cheung's model, R s were calculated and these values were found in increasing behaviour with the contribution of Si 3 N 4 insulator layer. In addition, the J R −V plot behaviours with linear dependence between ln(J R) vs. V 0.5 indicated that the dominant conduction mechanism in the reverse bias region was Schottky effect for both MS and MIS diodes. In the room temperature C−V 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 (∼2.5 V). The decrease in the negative capacitance corresponds to the increase of G/w.