The present disclosure provides a semiconductor structure. In accordance with some embodiments, the semiconductor structure includes a substrate, one or more fins each including a first semiconductor layer formed over the substrate, an oxide layer formed wrapping over an upper portion of each of the one or more fins, and a gate stack including a high-K (HK) dielectric layer and a metal gate (MG) electrode formed wrapping over the oxide layer. The first semiconductor layer may include silicon germanium (SiGex), and the oxide layer may include silicon germanium oxide (SiGexOy).