Attempts were made to optimize the electrochemical anodization process for the formation of high-density, regular and straight nanopore arrays on InP. The structure, shape and size of the pores were very sensitive to substrate orientations, electrolyte concentrations and anodization voltages. Among (1 1 1)A, (1 1 1)B and (0 0 1) substrate orientations, the most uniform and most straight nanopore arrays were obtained on (0 0 1) substrates at anodization voltages of 5-7 V by using 1.0-1.5 M HCl electrolyte containing HNO3. The pore depth could be controlled up to 80 mu m by the anodization time. (c) 2005 Elsevier B.V. All rights reserved.