It is identified that the development of hydrogen-silsesquioxane resist after electron-beam exposure, by using a 25% tetramethylammonium-hydroxide (TMAH) developer, almost stops after 1 min of development time and it severely limits the delineation of high-density nanometer-scale patterns. By using x-ray photoelectron spectroscopy, the authors identified that. this development-stopping phenomenon is due to the formation of a siloxane-type bond structure which is insoluble to the TMAH developer. Here, the authors propose a two-step development method that involves the removal process of siloxane layer using a dilute hydrofluoric acid between development processes. This method successfully eliminates the insoluble layer, thus generating isolated high-density dot patterns with 25 nm pitch. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3049482]