According to one embodiment, gate electrodes of a multi-gate field effect transistors and methods of making a gate electrode of a multi-gate field effect transistor are provided. The gate electrode can contain a semiconductor substrate; a dielectric layer over the semiconductor substrate; a fin over the dielectric layer; a gate insulating layer over the side surfaces of the fin; a gate electrode layer over the fin; and a polysilicon layer over the fin. The gate electrode does not contain a gate insulating layer over the upper surface of the dielectric layer except portions of the upper surface of the dielectric layer that contact with the side surfaces of the gate insulating layer formed over the side surface of the fin. In another embodiment, the gate electrode can contain an oxygen diffusion barrier layer or a first oxygen diffusion layer over the upper surface of the dielectric layer.