An electrical fuse and a method for forming the same are provided. The electrical fuse includes a dielectric layer over a shallow trench isolation region and a contact plug extending from a top surface of the dielectric layer to the shallow trench isolation region, wherein the contact plug comprises a middle portion substantially narrower than the two end portions. The contact plug forms a fuse element. The electrical fuse further includes two metal lines in a metallization layer on the dielectric layer, wherein each of the two metal lines is connected to different ones of the end portions of the contact plug.