This specification relates to an enhancement-type semiconductor device having a passivation layer formed using a photoelectrochemical (PEC) method, and a fabricating method thereof.To this end, a semiconductor device according to one exemplary embodiment includes a GaN layer, an AlGaN layer formed on the GaN layer, a p-GaN layer formed on the AlGaN layer, a gate electrode formed on the p-GaN layer, a source electrode and a drain electrode formed on a partial region of the AlGaN layer, and a passivation layer formed on a partial region of the AlGaN layer, the passivation layer formed between the source electrode and the gate electrode or between the gate electrode and the drain electrode, wherein the passivation layer is formed in a manner of oxidizing a part of the p-GaN layer.