This communication reports the formation of porous silicon (PS) by application of a positive potential on n- type silicon without illumination. PS films were formed in 1-ethyl-3-methylimidazolium oligofluorohydrogenate [EtMeIm(FH)(2.3)F] room-temperature ionic liquid, and the surface morphology strongly depended on the time and the applied potential. The results indicate that EtMeIm (FH)(2.3)F could be a nonaqueous solvent equivalent to hydrofluoric acid, allowing the formation of pores under anodic polarization. (c) 2007 The Electrochemical Society.