A semiconductor structure includes a first GAA transistor and a second GAA transistor. The first GAA transistor includes: a first top OD region, a first bottom OD region, and a first nanowire. A second GAA transistor includes: a second top OD region, a second bottom OD region, and a second nanowire. The first top OD region, the first bottom OD region, and the first nanowire are symmetrical with the second top OD region, the second bottom OD region, and the second nanowire respectively, the first GAA transistor is arranged to provide a first current to flow from the first top OD region to the first bottom OD region, and the second GAA transistor is arranged to provide a second current to flow from the second top OD region to the second bottom OD region.