Tungsten oxide semiconductor films for photoelectrochemical water-splitting applications, reactively sputtered at low temperatures (< 300 degrees C), have demonstrated photocurrents of 3.4 mA/cm(2) under AM 1.5 illumination in 0.33M H3PO4, exceeding published results for material pyrolytically fabricated at higher temperature, and approaching the theoretical maximum for tungsten trioxide based on optical absorption limits. The microstructural form of the reactively sputtered films, which is sensitive to the sputter process parameters, critically affects the photoconversion efficiency. It has also been determined that the sputtered WO3 films form true compact photoelectrodes in solution, with active charge generation and separation over the material's optical width. (c) 2006 The Electrochemical Society.