A photoetching method with N-fluoropyridinium salts is proposed in this study. Si is etched by applying N-fluoropyridinium salts to its surface and exposing the surface to light. The etched surface that uses liquid N-fluoropyridinium salts is smoother than when solid N-fluoropyridinium salts are used. The etching depth increases with exposure time. H-terminated hydrophobic Si is easier to etch than OH-terminated hydrophilic Si. SiF4 is produced by photoetching. This suggests that N-fluoropiridinium salts receive excited electrons from Si and supply Si with active F species. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3481770] All rights reserved.