This study presents voltage-dependent profile of interface traps in Au/n-Si structure with 2% graphene-cobalt-doped Ca3Co4Ga0.001Ox interfacial layer. Admittance measurements revealed capacitance-voltage (C-V) plots with typical regions of a metal-insulator-semiconductor structure through inversion, depletion, and accumulation regions. Frequency dispersion is observed in C-V plots and such behavior was explained with excess capacitance, which is associated with the density of interface traps (D-it) in the structure because larger D-it is observed when the measurements are held at low frequencies due to the fact that traps can follow the signal depending on their lifetime. D-it was also obtained using conductance method, which also provided lifetime of the traps. The difference between the values of D-it was attributed to the difference in extraction methods. Obtained results showed that Au/2% graphene-cobalt-doped Ca3Co4Ga0.001Ox/n-Si structure yields promising electrical characteristics when the structure is operated at high frequencies. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48399.