Photoelectrochemical (PEC) water splitting into hydrogen and oxygen is a promising strategy to absorb solar energy and directly convert it into a dense storage media in the form of chemical bonds. The continual development and improvement of individual components of PEC systems is critical towards increasing the solar to fuel efficiency of prototype devices. Within this context, we describe a study on the growth of wurtzite indium phosphide (InP) nanowire (NW) arrays on silicon substrates and their subsequent implementation as light absorbing photocathodes in PEC cells. The high onset potential (0.6 V vs. the reversible hydrogen electrode) and photocurrent (18 mA/cm2) of the InP photocathodes renders them as promising building blocks for high performance PEC cells. As a proof of concept for overall system integration, InP photocathodes were combined with a nanoporous bismuth vanadate (BiVO4) photoanode to generate an unassisted solar water splitting efficiency of 0.5%.