Herein, we report the high-temperature electrical characteristics of heterojunction diode fabricated based on n-Ga-doped ZnO nanowires/p-Silicon substrate. Various electronic properties such as rectification ratio, the effective barrier height, the diode ideality factor, etc. of the fabricated heterojunction diode at high temperature were investigated. The electrical characteristics were examined in the high-temperature range of 293 K–433 K in both reverse and forward biased conditions, which exhibited good stability over the entire temperature range. The observed current–voltage (I–V) studies confirmed three different conduction mechanisms for the fabricated heterojunction diodes, i.e., either field emission or tunneling, recombination-tunneling mechanism and the transport mechanism dominated by space-charge-limited current at the different regions. The observed electrical results exhibited fluctuations in the sensitivity of the quality factor of the heterojunction diode and consequently corresponding fluctuations in the resistance. The linear dependence of effective barrier height on quality factor can be attributed to the presence of some lateral inhomogeneities in the barrier height. The analysis of C–V data was conducted to deduce the value of barrier height of Schottky barrier for the fabricated heterojunction diode. Interestingly, the observed results assert the mismatch that occurs between the interface states and resulting capacitance of the fabricated heterojunction diode.