A semiconductor structure includes two circuit regions and two inner seal rings, each of which surrounds one of the circuit regions. Each inner seal ring has a substantially rectangular periphery with four interior corner stress relief (CSR) structures. The semiconductor structure further includes an outer seal ring surrounding the two inner seal rings. The outer seal ring has a substantially rectangular periphery without CSR structures at four interior corners of the outer seal ring. The outer seal ring includes a plurality of first fin structures located between each of the two inner seal rings and a respective short side of the outer seal ring. Each first fin structure is parallel with the respective short side of the outer seal ring. Lengths of the first fin structures gradually decrease along a direction from the inner seal rings to the respective short side of the outer seal ring.