Photovoltaic-photoelectrochemical (PV-PEC) cells based ion InGaP/GaAs show excellent prospects for efficient production of hydrogen by electrolysis of water using solar energy. We describe a combined close-spaced vapor transport (CSVT)/liquid-phase epitaxy (LPE) process co produce arrays of selectively-grown mesas of InGaP/GaAs on silicon substrates. Unlike other semiconductor devices, the PV-PEC cell is well suited for such selectively-grown, discontinuous heteroepitaxial films. Thus, this device application affords exploiting the potential advantages of selective epitaxy, namely, the substantial reduction of stress and defects caused by thermal expansion and lattice mismatch between the silicon substrate and III-V epilayers,