Thin films of indium nitride, InN, were produced by reactive magnetron DC sputtering. By post treatment in dinitrogen, N-2, in the temperature range 350-500 degrees C a set of films gradually going from InN to indium oxide, In2O3 was obtained (due to dioxygen impurities in the annealing gas). Those films were characterized by X-ray diffraction, optical-, resistivity- and photoelectrochemical measurements for the aim of direct watersplitting in a photoelectrochemical cell. Surprisingly, the caused change in the film composition by annealing gave no significant change in the room temperature resistivity, but the free electron density and the optical properties were affected. In 0.1 M NaOH annealing improved the photoresponse of the thin films. A pronounced optimum was observed for films annealed at 425 degrees C. Even for those films the quantum efficiency was low; at most 2% of the photons at 350 nm were transformed into readable photoelectrons. The onset wavelength for photocurrent was located around 600 run (2.1 eV), which is far off from the onset of absorption 900 nni (1.4 eV). (c) 2005 Elsevier B.V. All rights reserved.