The invention is suitable for a semiconductor device and provides a ring-gate structure field effect transistor, which comprises a substrate, a silicon dioxide layer deposited on the substrate, and grid, source and drain electrodes deposited on the silicon dioxide layer. The grid electrode comprises an active layer, an insulation layer wrapping around the active layer and a metal layer wrapping around the insulation layer, wherein the insulation layer is made of a high-dielectric-constant dielectric material. The ring-gate structure field effect transistor, by adopting the high-dielectric-constant dielectric material to serve as the insulation layer, has a good insulation property, can produce a higher field effect between the grid electrode and a substrate channel, can reduce transistor electric leakage amount and reduce device power consumption and heating, and enables the size of the transistor to be further reduced.