An interconnect structure is provided. The interconnect structure includes a first metal line and a second metal line surrounded by a first dielectric layer, a dielectric block over a portion of the first dielectric layer between the first metal line and the second metal line, and a second dielectric layer over the dielectric block, the first metal line and the second metal line. A bottom surface of the second dielectric layer is lower than a top surface of the dielectric block. The interconnect structure also includes a first via surrounded by the second dielectric layer and electrically connected to the first metal line.