The band edges of p-GaInP2 are observed to migrate toward negative potentials during current flow under illumination in solutions with pH ranging from 1 to 14.5. The migration is not caused by a change in the pH of the semiconductor microenvironment but is a result of accumulation of photogenerated electrons at the p-GaInP2/water interface due to poor interfacial kinetics. This less than optimal interfacial charge-transfer rate can be catalyzed by treating the surface with transition-metal ions (e.g., Ru-III, Rh-III, Co-III, Os-III) which results in a suppression of band edge migration. As compared to an unmodified p-GaInP2 surface, the metal-ion treatment does not induce any appreciable band edge shift in the dark but effectively suppresses the band edge migration under illumination. Rum and RhIII are found to act as better hydrogen-evolution catalysts than electrodeposited Pt.