A method of fabricating a MOS transistor, and the MOS transistor fabricated by the method, includes providing a substrate, forming a predetermined layer having a non-planar surface on the substrate, the predetermined layer including at least one active region, forming a gate electrode material layer on the non-planar, predetermined layer, forming a material layer and a hard mask layer on an entire surface of the gate electrode material layer, and planarizing a top surface of the material layer to form a planarized material layer, forming a photoresist pattern on the planarized material layer and the hard mask layer to pattern the gate electrode material layer, forming a hard mask pattern by etching the hard mask layer using the photoresist pattern as an etching mask, and forming a predetermined pattern by etching the planarized material layer and the gate electrode material layer according to a shape of the hard mask pattern.