In a method of manufacturing a gate-all-around field effect transistor, a trench is formed over a substrate. Nano-tube structures are arranged into the trench, each of which includes a carbon nanotube (CNT) having a gate dielectric layer wrapping around the CNT and a gate electrode layer over the gate dielectric layer. An anchor layer is formed in the trench. A part of the anchor layer is removed at a source/drain (S/D) region. The gate electrode layer and the gate dielectric layer are removed at the S/D region, thereby exposing a part of the CNT at the S/D region. An S/D electrode layer is formed on the exposed part of the CNT. A part of the anchor layer is removed at a gate region, thereby exposing a part of the gate electrode layer of the gate structure. A gate contact layer is formed on the exposed part of the gate electrode layer.