The energy dependence of the interface states (N-ss) and relaxation time (tau) and capture cross section (sigma(p)) of N-ss in (Au/PVC+TCNQ/p-Si) heterojunction were investigated using high-low frequency capacitance (C-HF-C-LF) and conductance method, which contains many capacitance/conductance [C/(G/omega)-V] plots. The C value of the heterojunction increases with decreasing frequency as almost exponentially due to the existence of N-ss between metal and semiconductor. The N-ss and tau values have been obtained in the (0.053-E-v)-(0.785-E-v)-eV energy range by considering the voltage-dependent surface potential obtained from the lowest measurable frequency C-V curve at 1 kHz. The magnitude of N-ss ranges from 3.88x10(12) eV(-1)cm(-2) to 3.24 x 10(12) eV(-1)cm(-2). In the same energy range, the value of tau ranges from 5.73x10(-5) to 1.58x10(-4) s and shows almost an exponential increase with increasing bias from the top of the valance band edge toward the midgap of semiconductor. The obtained N-ss values from C-HF-C-LF and conductance methods are in good agreement with each other for the heterojunction. As a result, the mean value of N-ss was found on the order of 10(12) eV(-1)cm(-2) and this value is very suitable for an electronic device.