The d.c. electrical properties of gold/nickel phthalocyanine/indium (Au/NiPc/In) thin film structures have been investigated. Three-layered devices were fabricated utilising a sequential vacuum sublimation technique. At low voltages, current density in the forward direction was found to obey the diode equation, while for higher voltage levels, conduction was dominated by a space-charge-limited conduction (SCLC) mechanism. In the reverse bias direction a transition from electrode-limited to a bulk-limited conduction process was identified. After prolonged exposure of the sample to dry air a weak polarity dependence of conduction was observed. Analysis of the experimental data under reverse bias suggests a transition from electrode-limited to a bulk-limited conduction process for lower and higher applied voltages, respectively. After annealing of the samples at 393 K in vacuum for 20 min, a strong rectifying behaviour was evident. Results were interpreted in terms of an O-2 adsorption process at the NiPc/In interface. Hole trapping parameters together with various junction properties have been also reported and analysed.