The present invention provides a method of forming a semiconductor structure. A wafer with a dicing region is provided, the dicing region comprises a central region, a middle region surrounds the central region, and a peripheral region surrounds the middle region. Next, an aligning mark is formed in the dicing region, wherein the aligning mark is a mirror symmetrical pattern and comprises a plurality of second patterns in the middle region and a plurality of third patterns in the third region, each third pattern has a plurality of lines and the lines comprises a plurality of inner lines which are formed by a sidewall image transfer (SIT) process.