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This work demonstrates the modification of electrical parameters of the Au/n-GaN Schottky junction (SJ) by a thin magnetite metal (Fe 3 O 4) interlayer in between the Au and n-GaN substrates. The current-voltage (I-V), voltage-dependent capacitance-frequency (C-f) and conductance-frequency (G-f) characteristics of the Au/Fe 3 O 4 /n-GaN heterojunction (HJ) are systematically studied. Using statistical analysis, the mean barrier heights and ideality factors are found to be 0.70 eV and 1.62 for the SJ and 0.84 eV and 1.87 for the HJ, respectively. It is noticed that the mean barrier height of Au/ Fe 3 O 4 /n-GaN HJ increases as compared that of the Au/n-GaN SJ, indicating the Fe 3 O 4 interlayer modified the barrier height. The SJ revealed a transition from Poole-Frenkel emission at low voltages to Schottky emission at high voltages. However, the HJ exhibited Schottky emission over whole voltage range. It is observed that the higher values of capacitance decrease at low frequencies that are attributed to the excess capacitance resulting from the interface states in equilibrium with the n-GaN which could respond the ac signal. The interface states density (N SS) and relaxation time (τ) of the Au/Fe 3 O 4 /n-GaN HJ are estimated from C-f plots, respectively. The N SS reveals that the interface states decrease with voltage from the bottom of the conduction band toward the mid-gap. Keywords Fe 3 O 4 interlayer • n-GaN substrate • Voltage-dependent C-f and G-f properties • Interface state density • Relaxation time