The present disclosure describes a fin-like field-effect transistor (FinFET). The device includes one or more fin structures over a substrate, each with source/drain (S/D) features and a high-k/metal gate (HK/MG). A first HK/MG in a first gate region wraps over an upper portion of a first fin structure, the first fin structure including an epitaxial silicon (Si) layer as its upper portion and an epitaxial growth silicon germanium (SiGe), with a silicon germanium oxide (SiGeO) feature at its outer layer, as its middle portion, and the substrate as its bottom portion. A second HK/MG in a second gate region, wraps over an upper portion of a second fin structure, the second fin structure including an epitaxial SiGe layer as its upper portion, an epitaxial Si layer as it upper middle portion, an epitaxial SiGe layer as its lower middle portion, and the substrate as its bottom portion.