A method for fabrication of a semiconductor structure according to some embodiments of the present disclosure comprises following steps. A first mandrel is formed over a target layer over a substrate, wherein the first mandrel comprises a mandrel island connecting a first mandrel strip and a second mandrel strip. A first spacer is formed along first and second sidewalls of the mandrel island, the first mandrel strip, and the second mandrel strip. The first mandrel is then removed, and the target layer is patterned with the first spacer remains over the target layer. The first mandrel strip and the second mandrel strip are misaligned from one another.