We explored the selective wet silylation of noncrosslinked areas of epoxidized photoresists using chlorosilanes. Emphasis was placed on the Si uptake of the epoxy films when controlled low levels of water were incorporated into the silylation solution. Fourier transform infrared measurements and oxygen-plasma resistance data with in situ laser interferometry and multiwavelength ellipsometry are presented. The fine tuning of the moisture level was found to be crucial for the generation of satisfactory and reproducible structures. The optimized version of the process was shown to be useful for epoxy-based dry micromachining. Overall, an attractive positive-tone process is presented as an alternative to the usual negative-tone process for commercial epoxy resists. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2189-2195, 2010