The present disclosure relates to a method for fabricating a field-effect transistor structure on a substrate. The method includes forming a first semiconductor structure on the substrate, forming above the first semiconductor structure a gate structure that comprises a spacer layer laterally terminating the gate structure and has a lower etch rate than the first semiconductor structure with respect to a predetermined etchant, forming an undercut below the spacer layer by recessing the first semiconductor structure using the etchant, the undercut extending laterally below the spacer layer by not more than the thickness of the spacer layer, forming on the first semiconductor structure a second semiconductor structure filling the undercut, and forming a third semiconductor structure above the first semiconductor structure, wherein one of the second and third semiconductor structures forms the source of the field-effect transistor structure and the other one forms the drain.