Using density-functional theory, we investigate the effects of surface modifications on electronic properties of GaN/InN core/shell nanowires (CSNWs) with different core radii and shell thicknesses in triangular and hexagonal shapes. Our calculations demonstrate that surface modifications with H and F substantially modulate the band gaps and induce the separation of electrons and holes. The results elucidate that surface modifications change electronic structures of CSNWs with a transition from type-I band alignment to quasi-type-II, which could open a new way in the field of renewable energy applications. (C) 2011 Elsevier B.V. All rights reserved.