GaAs substrates were anodized in the (NH4)(2)SO4 electrolyte with various fluoride concentrations. Scanning electron microscope (SEM) observation showed that highly regular honeycomb hollows were formed on the substrates anodized in the (NH4)(2)SO4 electrolyte with a small amount of HF concentration. The regularity of hollows decreased with the increase of HF concentration. The average diameter of hollows increased with increasing anodizing voltage. The regularity of hollow diameters increased with the increase of anodizing time, irrespective of the anodizing voltage. Cross-sectional SEM image showed that the average depth of regular hollows was about 5 nm. In addition to the peak in the region of fundamental adsorption of GaAs with the peak wavelength at about 870 nm, photoluminescence spectra of samples anodized in the (NH4)(2)SO4 electrolyte with HF concentration of 0.5 ml showed several peaks at about 610, 635, 670 and 720 nm. (C) 2014 Elsevier B. V. All rights reserved.