Porous gallium phosphide was produced by anodic etching of n-type GaP in an aqueous solution of 1 M HNO3. At potentials lower than 15.5 V, yellow porous samples were obtained, of which the pore size was around 45% larger than the pores obtained in 0.5 M H2SO4. At potentials around 15.5 V electropolishing occurred. No pores formed when GaP was etched at potentials in this range. At potentials higher than approximately 15.5 V the current density increased strongly with increasing potential, and very large pores formed. It was found that NO3- and SO42- only play a role in the chemical dissolution of the oxide layer that forms during etching. (c) 2006 The Electrochemical Society.