A semiconductor device includes a substrate, a gate structure, a first impurity region, and a second impurity region. The gate structure may cross over a first active region and a second active region of the substrate. The first insulation structure including a first insulation material may be formed on the first active region, and may be spaced apart from opposite sides of the gate structure. The second insulation structure including a second insulation material different from the first insulation material may be formed on the second active region, and may be spaced apart from opposite sides of the gate structure. The first impurity region may be formed at a portion of the first active region between the gate structure and the first insulation structure, and may be doped with p-type impurities. The second impurity region may be formed at a portion of the second active region between the gate structure and the second insulation structure, and may be doped with n-type impurities. A stress may be applied onto a channel region of a transistor, so that the semiconductor device may have good electrical characteristics.