Epilayer samples of GaInPN with a stoichiometry of Ga.962In.038P.976N.024 and Ga.95In.05P.975N.025 were grown by metallorganic chemical vapor deposition and were photoelectrochemically characterized to determine their potential to photoelectrolyze water. The materials had direct transition bandgap energies of similar to 2.0 eV, as determined by photocurrent spectroscopy; however, the measured flatband potentials were several hundred millivolts too negative for unbiased water splitting. Stability was assessed by operating the electrodes as photocathodes for 24 h and qualitatively evaluated by probing the amount of surface etching with a stylus profilometer. Quantitative evaluation was done by measuring the concentration of gallium in the corrosion test electrolyte using inductively coupled plasma mass spectrometry. Results were compared to similarly treated GaP and GaInP2 samples for context. (C) 2008 The Electrochemical Society.