One of the crucial parameters dictating the efficiency of photoelectrochemical water-splitting is the semiconductor band edge alignment with respect to hydrogen and oxygen redox potentials. Despite the importance of metal oxides in their use as photoelectrodes, studies to control the band edge alignment in aqueous solution have been limited predominantly to compound semiconductors with modulation ranges limited to a few hundred mV. We report our studies demonstrating the ability to modulate the flat band potential of oxide photoanodes by as much as 1.3 V, using the insertion of subsurface electrostatic dipoles near a Nb-doped SrTiO3/aqueous electrolyte interface. The tunable range achieved in this study far exceeds previous reports in any semiconductor/aqueous electrolyte system and sugges ts a general design strategy for highly efficient oxide photoelectrodes. Show Partial Abstract