In this study, Au–4H-[Formula: see text]-SiC metal–semiconductor (MS) and Au–Al2O3–4H-[Formula: see text]-SiC metal–insulator–semiconductor (MIS) devices were fabricated to examine the effects on the performance of electronic devices of interfacial insulating materials. In order to determine the dielectric properties, capacitance/conductance–voltage ([Formula: see text]–[Formula: see text] measurements were realized in a wide range of voltages ([Formula: see text]3.0 V)–(11.0 V). Current–voltage ([Formula: see text]–[Formula: see text] measurements to obtain the electric properties were realized at [Formula: see text][Formula: see text]V. Moreover, both the energy distributions of surface states ([Formula: see text] and series resistance ([Formula: see text] were obtained from the [Formula: see text]–[Formula: see text] data. Obtained results provided that series resistance originating from interfacial layer (Al2O[Formula: see text] was more effective on the [Formula: see text]–[Formula: see text] and [Formula: see text]–[Formula: see text] characteristics which must be taken into account in the calculation of main electrical parameters. The rectification ratio (RR) and shunt resistance ([Formula: see text] of the MIS device were almost 103 times greater than those of the MS structure. Using Al2O3 between Au and 4H-[Formula: see text]-SiC also led to an increase in the value of barrier height (BH) and a decrease in the value of ideality factor ([Formula: see text]. These results confirmed that Al2O3 layer leads to an increase in the performance of MS device with respect to low values of [Formula: see text], reverse saturation current ([Formula: see text] and [Formula: see text] and high values of RR, [Formula: see text] and BH.