A method for manufacturing a field effect transistor of a non-planar type, comprising providing a substrate having an initially planar front main surface, and providing shallow trench isolation structures in the substrate on the front surface, thereby defining a plurality of fin structures in the substrate between the shallow trench isolation structures. Top surfaces of the shallow trench isolation structures and the fin structures abut on a common planar surface, and sidewalls of the fin structures are fully concealed by the shallow trench isolation structures. The method also includes forming a dummy gate structure over a central portion of the plurality of fin structures on the common planar surface, forming dielectric spacer structures around the dummy gate structure, and removing the dummy gate structure, thereby leaving a gate trench defined by the dielectric spacer structures. Further, the method includes removing an upper portion of at least two shallow trench isolation structures to expose at least a portion of the sidewalls of the fin structures within the gate trench, and forming a final gate stack in the gate trench.