A semiconductor device is disclosed. The semiconductor device includes: a substrate; a first tensile dielectric layer on the substrate; a metal gate in the first tensile dielectric layer; a second tensile dielectric layer on the first tensile dielectric layer; and a contact plug in the first tensile dielectric layer and the second tensile dielectric layer. Preferably, the top surface of the contact plug is even with the top surface of the second tensile dielectric layer, and a carbon content of the second tensile dielectric layer is greater than the carbon content of the first tensile dielectric layer.