A field effect transistor (FET) and a manufacturing method thereof are provided. The FET includes a substrate, a fin bump, an insulating layer, a charge trapping structure and a gate structure. The fin bump is disposed on the substrate. The insulating layer is disposed on the substrate and located at two sides of the fin bump. The charge trapping structure is disposed on the insulating layer and located at least one side of the fin bump. A cross-section of the charge trapping structure is L-shaped. The gate structure covers the fin bump and the charge trapping structure.