p-Type gallium phosphide (GaP) electrodes have been sensitized by triarylmethane dyes physisorbed from aqueous solutions. This work is the first to show light-stimulated hole injection from an adsorbed molecular chromophore on native GaP surfaces. Freshly etched p-GaP(100) and p-GaP(111)­A electrodes were loaded with physisorbed dye by brief soaking in solutions of Fast Green. X-ray photoelectron spectroscopy, corroborated by Auger electron spectroscopy, indicated that such treatments yield undetectable surface coverages. However, steady-state photoelectrochemical responses consistently showed that sub-bandgap photoresponses were commensurate with light absorption by the adsorbed dye. The photoresponse characteristics were clearly insensitive to the identity and amount of intended redox mediators dissolved in solution at low light intensities. Instead, the data suggest electrochemically active surface states related to the cathodic degradation of GaP can accept electrons from photoexcited physisorbed dye. Measurements at high illumination intensities showed sensitivity toward redox mediators in solution, indicating that the conventional mode of dye regeneration by redox species in solution is possible with p-GaP. Separate measurements with covalently modified p-GaP(111)­A photoelectrodes further suggested that deliberate modification to minimize/eliminate surface states is also possible. Collectively, this work indicates that although some types of dye readily adsorb onto native GaP interfaces, the low dye loadings and the susceptibility of the interface to chemical attack during the sensitization process argue against using bare p-GaP photocathodes with physisorbed triarylmethane dyes. Instead, these studies suggest that dye-sensitized photocathodes based on p-GaP require deliberate surface chemical modification methods to overcome the low loading and inhibit unwanted charge transfer between the surface and the photoexcited dye.