Provided are a semiconductor device configured to block a physical diffusion path by forming an oxide layer between barrier layers to prevent impurities from being diffused through the physical diffusion path between the barrier layers, and a method for fabricating the semiconductor device. The semiconductor device includes a gate insulation layer formed on a substrate, a first barrier layer formed on the gate insulation layer, an oxide layer formed on the first barrier layer, the oxide layer including an oxide formed by oxidizing a material included in the first barrier layer, a second barrier layer formed on the oxide layer, a gate electrode formed on the second barrier layer, and source/drains disposed at opposite sides of the gate electrode in the substrate.