A two-step chlorination/alkylation method was used to introduce -CnH2n+1 (n = 1-6) functionality onto single-crystal, (111)-oriented, n-type Si surfaces. H-terminated Si photoanodes were unstable under illumination in contact with an aqueous 0.35 M K4Fe(CN)(6)-0.05 M K3Fe(CN)(6) electrolyte. Such electrodes displayed low open-circuit voltages and exhibited a pronounced time-dependent deterioration in their current density vs potential characteristics due to anodic oxidation. In contrast, Si surfaces functionalized with -CH3 and -C2H5 groups displayed significant improvements in stability while displaying excellent electrochemical properties when used as photoelectrodes in the aqueous Fe(CN)(6)(3-/4-) electrolyte.