This work presents progress in the development of stable gallium phosphide (GaP) interfaces capable of undergoing subsequent reactions by introducing an organic monolayer. The context of this work is the use of p-GaP in a fuel forming photoelectrochemical cell. Semiconductor photoelectrodes require specific bulk and surface properties. Gallium phosphide has a band gap of 2.26 eV that allows for absorption in the visible range while the band edge positions make processes like hydrogen and carbon dioxide reduction possible. However, the surface is susceptible to rapid degradation via formation of a native oxide. Surface functionalization techniques provide means to passivate the semiconductor/liquid interface against degradation. In addition, by introducing organic monolayers on semiconductor surfaces subsequent reactions can be performed to further tailor the semiconductor interface as desired. This work focuses on using Grignard chemistry to chemically passivate the gallium phosphide surface via a formation of a gallium-carbon bond. To further alter the interface, reactive handles consisting of either hydroxyl or amine groups are introduced. These functional groups are used to covalently couple dyes to the gallium phosphide previously shown to photosensitize the semiconductor. The stability of the covalent attachment is investigate as a function of pH. Covalent attachment is showed using X-ray photoelectron spectroscopy while gallium phosphide dye sensitization is probed by analyzing the photoresponse pass the band gap.