Abstract Current density-voltage characteristics of nickel phthalocyanine thin films sandwiched between ohmic gold electrodes have been investigated. Ohmic conduction was predominant at low applied fields, with the free hole concentration dependent on subsequent sample treatment. Freshly prepared samples show a room-temperature free hole concentration p 07.25× 1018m−3, whereas samples heat-treated at 500 K. have a much lower value, of approximately 2.35 × 1014m−3. The high-field conductivity was associated with space-charge-limited conductivity (SCLC); different trapping modes were found to dominate this type of conduction, depending on post-deposition sample treatment. For freshly prepared samples the SCLC was dominated by a single trapping level situated at E t0.58eV above the valence band edge. Traps distributed exponentially with energy in the forbidden energy gap of the material dominate the J-V characteristics of the heat-treated samples, as indicated by a J∝V n relationship, with n>2. Trap concen...