Semiconductor structures and fabrication methods are provided. An exemplary fabrication method includes providing a semiconductor substrate having a fin material layer on the semiconductor substrate; forming an isolation material layer having a bandgap greater than a bandgap of the fin material layer on the fin material layer; and forming a stacked channel material layer on the isolation material layer. The stacked channel material layer includes a sacrificial material layer and a channel material layer on the sacrificial material layer. The method also includes etching the stacked channel material layer, the isolation material layer and the fin material layer to form fins protruding from the semiconductor substrate, an isolation layer on the fins and a stacked channel layer on the isolation layer. The stacked channel layer includes a sacrificial layer and a channel layer on the sacrificial material layer.