This specification is directed to a semiconductor device capable of reducing a leakage current by forming a first GaN layer including a plurality of GaN layers and FexNy layers interposed between the plurality of GaN layers, in a semiconductor device having the first GaN layer, an AlGaN layer, a second GaN layer, a gate electrode, a source electrode and a drain electrode which are deposited in a sequential manner, and a fabricating method thereof.To this end, a semiconductor device according to one exemplary embodiment includes a first GaN layer, an AlGaN layer on the first GaN layer, a second GaN layer on the AlGaN layer, and a source electrode, a drain electrode and a gate electrode formed on a portion of the second GaN layer, wherein the first GaN layer comprises a plurality of GaN layers and FexNy layers interposed between the plurality of GaN layers.