The fin 110 may comprise at least a semiconductor material selected from the group consisting of silicon, silicon-germanium (Si_1-xGe_x), germanium, and III-V compound semiconductors such as gallium arsenide, indium gallium arsenide (In_mGa_1-mAs), indium arsenide, indium phosphide, and indium antimonide. The fin 110 may comprise strained Si_1-xGe_x formed on Si, or strained Si formed on relaxed silicon-germanium. In an embodiment, the fin 110 comprises strained Si_1-xGe_x and the substrate 102 comprises a relaxed or partially relaxed silicon germanium alloy Si_1-rGe_r layer, where the germanium mole fraction r is smaller than x. By selecting x to be larger than r, the natural lattice constant of the Si_1-xGe_x channel is larger than that of Si_1-rGe_r, and the Si_1-xGe_x channel is under compressive stress or strain. In embodiments, the compressive strain in the channel in the longitudinal direction is larger than 0.5%, such as larger than 1%. In embodiments, the substrate 102 may also comprise a silicon oxide (SiO₂) layer (i.e. silicon-on-insulator substrate), and the fin 110 may be formed from a silicon-on-insulator wafer. In the illustrated embodiment, the fin sidewall surfaces are of (110) crystal orientation and the fin top surface is of (100) crystal orientation. The fin sidewall surfaces may be of other crystal orientations such as (551). Other configurations and shapes of the fin 110 are possible and are within the scope of the present disclosure.