The surface of epi layer p-GaInP2 electrodes was treated using 8-quinolinol, cupferron, and ferrocyanide, producing a modified surface directed at varying the Helmholtz layer charge. Mott-Schottky and photocurrent-voltage measurements were carried out to determine if there was any shift in the flatband potential or change in the onset of photocurrent due to the altered surface charge. Treatments with 8-quinolinol and cupferron were found to shift the flatband to more positive potentials; treatments with ferrocyanide produced a negative shift. The quinolate-modified interface had flatband potentials that were pH independent in the range 5 through 8. Photoluminescence studies on electrodes that were etched, treated with 8-quinolinol, and exposed to air for long periods showed no degradation of the luminescence intensity or photoluminescence decay time, in contrast to untreated electrodes.