Semiconductor devices and methods of manufacturing the same are disclosed. The semiconductor device a gate dielectric pattern on a substrate and a gate electrode on the gate dielectric pattern opposite the substrate. The gate electrode includes a first conductive pattern disposed on the gate dielectric pattern and including aluminum, and a second conductive pattern disposed between the first conductive pattern and the gate dielectric pattern. The second conductive pattern has an aluminum concentration that is higher than an aluminum concentration of the first conductive pattern. The second conductive pattern may be thicker than the first conductive pattern.