Tungsten carbide (WC) thin films are sputter deposited using a WC target on different substrates such as Si (111), Si (100), sapphire (0001), and Si (111) coated with Ti thin film. These films are characterized for their crystallographic structure, composition, electrical resistivity, optical transmittance and oxidation resistance in order to use WC as thermally stable electrodes for diamond devices. Preferentially (100) oriented cubic WC1-x thin films are obtained at room temperature, irrespective of the various deposition conditions and substrates. The electrical resistivity of the films is about 200-300 mu Omega cm. No deterioration of the properties occurs after annealing at 500 degrees C in argon ambient. However, the films suffer from decomposition at 800 degrees C with the depletion of carbon. The well characterized WC and Ti/WC bilayer are used as Schottky and ohmic contacts of diamond photodiodes, respectively. The excellent Schottky properties with rectifying ratio of 108 and reverse leakage current lower than 10(-14) A are maintained upon annealing at 500 degrees C for 4 h. This work indicates that the WC-based Schottky and ohmic contacts are promising in diamond optoelectronic devices for high-temperature applications. (c) 2006 Anterican Vacuum Society.