Provided is a semiconductor structure. The semiconductor structure is formed on a substrate, and includes a first region and a second region surrounded by the first region. The first region has a first pattern density, and the second region has a second pattern density. The first pattern density is smaller than the second pattern density. The second region includes a central region and a boundary region. The central region has a first critical dimension, and the boundary region has a second critical dimension. Variation between the first critical dimension and the second critical dimension is smaller than 6.5%.