A methodology for forming a single diffusion break structure in a FinFET device involves localized, in situ oxidation of a portion of a semiconductor fin. Fin oxidation within a fin cut region may be preceded by the formation of epitaxial source/drain regions over the fin, as well as by a gate cut module, where portions of a sacrificial gate that straddle the fin are replaced by an isolation layer. Localized oxidation of the fin enables the stress state in adjacent, un-oxidized portions of the fin to be retained, which may beneficially impact carrier mobility and hence conductivity within channel portions of the fin.