Provided are a semiconductor device with a T-gate electrode capable of improving stability and a high frequency characteristic of the semiconductor device by reducing source resistance, parasitic capacitance, and gate resistance and a method of fabricating the same. In the semiconductor device, in order to form source and drain electrodes and the T-gate electrode on a substrate, first and second protective layers constructed with silicon oxide layers or silicon nitride layers are formed on sides of a supporting part under a head part of the T-gate electrode, and the second protective layer constructed with a silicon oxide layer or silicon nitride layer is formed on sides of the source and drain electrodes. Accordingly, it is possible to protect an activated region of the semiconductor device and reduce gate-drain parasitic capacitance and gate-source parasitic capacitance.