Semiconductor devices and fabrication methods are provided. A semiconductor substrate is provided having dummy gate structures formed thereon. A stress layer is formed in the semiconductor substrate between adjacent dummy gate structures. A first dielectric layer is formed on the semiconductor substrate, the stress layers, and the sidewall spacers of the dummy gate structures, exposing dummy gate electrode layers. Gate structures are formed in the dielectric layer to replace the dummy gate structures. The gate structures include functional gate structures and at least one non-functional gate structure. The at least one non-functional gate structure is removed to form at least one second opening in the first dielectric layer. At least one third opening is formed in the semiconductor substrate at a bottom of the at least one second opening. A second dielectric layer is formed in the at least one second opening and the at least one third opening.