The photoelectrochemical behavior of GaSb has been investigated in aqueous NaOH, NaCl, and HCl solutions. Despite the relatively narrow bandgap, the photo-oxidation and dissolution process dominated the behavior of n-GaSb at potentials positive of the flatband potential (V-FB). At high pH and sufficient solution agitation, the etch rate was proportional to light intensity. At potentials 0.5 V positive of V-FB, a tunneling oxidation current developed resulting in an etch process that was independent of the light intensity. XPS analysis of the etched surface suggested that an increase in the dissolution rate of antimony oxides took place at high pH and solution agitation. The formation of an antimony oxide film resulted in surface passivation. Because of the relatively negative flatband potential of n-GaSb, oxygen was reduced at the same potential that n-GaSb was photo-oxidized. Thus, at the flatband potential, an open-circuit photoetch rate of 1 mu m/min was observed in an air-saturated solution.