Structural and electrical properties of the CuO films and the ZnO/CuO heterojunctions prepared by chemical bath deposition (CBD) technique involving thermal annealing process were studied by scanning electron microscope observation, X-ray diffraction, current density-voltage (J-V) and capacitance-voltage (C-V) measurements. The as-grown CuO films showed p-type conduction after annealing in the air at temperatures (T-A) ranging from 200 to 300 degrees C. The n-ZnO/p-CuO heterojunctions were composed of the columnar CuO grains and the ZnO nanorods (NRs) and their J-V curves exhibited rectifying characteristics with large diode ideality, factors (n) and leakage currents. The insertion of the ZnO intermediate layer prepared by dip-coating (denoted by "Dip-coating ZnO") between the ZnO and CuO layers was found to be effective for reducing the n value and suppressing the leakage current. The threshold voltage (V-th), built-in potential (V-bi) and n value of the ZnO/Dip-coating ZnO/CuO heterojunction were strongly dependent on T-A and showed minima around T-A=250-300 degrees C. Taking into account the fact that the rectification ratios of the forward current to the reverse current were very low at the same T-A region, the low V-th and V-bi values are attributed to the tunneling process through the interface states introduced by the structural imperfection. (C) 2014 Elsevier B.V. All rights reserved.