A field effect transistor having a T- or Γ-shaped fine gate electrode of which a head portion is wider than a foot portion, and a method for manufacturing the field effect transistor, are provided. A void is formed between the head portion of the gate electrode and a semiconductor substrate using an insulating layer having a multi-layer structure with different etch rates. Since parasitic capacitance between the gate electrode and the semiconductor substrate is reduced by the void, the head portion of the gate electrode can be made large so that gate resistance can be reduced. In addition, since the height of the gate electrode can be adjusted by adjusting the thickness of the insulating layer, device performance as well as process uniformity and repeatability can be improved.