Solar energy is one of the most abundant renewable energy sources. However, the diurnal variation of the sun as well as seasonal and weather effects, limits the widespread global implementation of solar energy. Thus, cost-effective energy storage is critical to overcome the intermittent nature of solar energy available on the earth. Photoelectrolysis of water to oxygen and hydrogen fuel is a promising large-scale solution to store solar energy in a dense and portable form. Photoelectrochemical water-splitting research strives to develop a semiconductor photoelectrode with both high efficiency and long-term stability. III–V semiconductors are among the most promising materials for high efficiency solar fuels applications. However, they suffer from severe instability in acidic and alkaline electrolyte and fundamental understanding of their corrosion mechanism is of significant importance for the solar fuels community. This dissertation is focused on study of gallium based III-V semiconductors for water splitting systems. Corrosion of n-GaP, a promising III–V material for tandem top subcells, was investigated in strongly acidic electrolyte using an in-situ UV-Vis spectroscopy technique to interpret the corrosion process in conjunction with SEM and XPS characterization. Further, photocorrosion of n-GaAs, one of the most well-developed III-V semiconductors was studied. Three type of Ir, OER co-catalyst, were tested to explore their affect on photocorrosion of n-GaAs photoanodes. Synthesis of ternary III-V alloys enable us to tune the band gap and band edge positions of III-V semiconductors according to the requirements of desired PEC system. Herein, optical and electrical properties of a novel III-V ternary alloy GaSbxP(1-x), synthesized by halide vapor phase epitaxy is also investigated with various characterization techniques such as diffuse reflectance spectroscopy, X-ray diffraction spectroscopy, and Hall effect measurement.