A new single-layer, dry developable chemically amplified resist is described. The resist consists of poly(4-hydroxystyrene), 1,2,4,5- tetra(acetoxymethyl)benzene and triphenylsulfonium hexafluoroantimonate, and functions via crosslinking as a result of an acid-catalysed electrophilic aromatic substitution reaction. In contrast to the normal wet resist development process that leads to a negative-tone image, a gas-phase modification of the exposed polymer film, followed by reactive oxygen etching, leads to a positive-tone image. The post-exposure modification is accomplished using gaseous 1,1,1,3,3,3-hexamethyldisilazane, a reagent that is able to diffuse selectively into the non-exposed, non-crosslinked regions of the polymer film to react with the poly(4-hydroxystyrene) and form silyl ethers. Dry-development of the treated film in an O2 plasma removes those areas of the film that have remained unsilylated, producing a positive-tone relief image.