The present invention provides a semiconductor device and a method for manufacturing the same. The method for manufacturing the semiconductor device comprises: providing a silicon substrate having a gate stack structure formed thereon and having {100} crystal indices; forming an interlayer dielectric layer coving a top surface of the silicon substrate; forming a first trench in the interlayer dielectric layer and/or in the gate stack structure, the first trench having an extension direction being along crystal direction and perpendicular to that of the gate stack structure; and filling the first trench with a first dielectric layer, wherein the first dielectric layer is a tensile stress dielectric layer. The present invention introduces a tensile stress in the transverse direction of a channel region by using a simple process, which improves the response speed and performance of semiconductor devices.