A mark pattern includes unit cells immediately adjacent to each other and arranged in a form of dot matrix to form a register mark or an identification code, wherein each unit cell has configuration identical to functional devices of pMOS and nMOS, and each unit cell includes a first active region, a second active region isolated from the first active region, and first gate structures extending along a first direction and are arranged along a second direction perpendicular to the first direction, and the first gate structures straddling the first active region and the second active region, contact structures disposed between the first gate structures on the first active region and the second active region, and via structures disposed on the contact structures and two opposite ends of the first gate structures.