Provided is a semiconductor device with a field effect transistor. The semiconductor device includes a substrate, an active pattern on the substrate, a gate electrode crossing the active pattern and a capping structure on the gate electrode. The capping structure includes first and second capping patterns that are sequentially stacked on the gate electrode. The second capping pattern completely covers a top surface of the first capping pattern, and a dielectric constant of the second capping pattern is greater than that of the first capping pattern.