Alkyl monolayer (octadecyl) was formed on a hydrogen-terminated Si(111) (H-Si(111)) electrode via Si-C covalent bond by photoanodic reaction with C18H37MgCl in THF solution. The formation of the organic monolayer was confirmed by attenuated total reflection (ATR) FT-IR spectroscopy. This process was applied to a one-step patterning of an organic monolayer on a H-Si(111) by illuminating the H-Si(111) electrode through photomask in a C18H37MgCI/THF solution at positive potential. The formation of the pattern reflecting the shape of the photomask was confirmed by SEM observations. (c) 2006 Elsevier B.V. All rights reserved.