The anodic dissolution of silicon in dilute HF electrolyte exhibits some anisotropy in the region of the first electropolishing plateau. This anisotropy can plausibly be assigned to an orientation-dependent surface chemistry. The silicon\dilute fluoride electrolyte interface has been investigated by in situ infrared vibrational spectroscopy in the differential mode, in the potential region where the surface turns from hydrogenated to oxidised. Silicon surfaces of different orientations exhibit closely similar behaviour. However, careful analysis of the nu OH region reveals a significant difference in the concentration of SiOH groups at (100)- and (111)-oriented Si surfaces. This observation points to the key role of the SiOH groups in determining the anisotropic behaviour of the electrochemical dissolution of silicon. (C) 2003 Elsevier B.V. All rights reserved.