A semiconductor device includes a first region, a second region, a third region, and a fourth region. The first region includes a first portion of an N-well and a plurality of P-type transistors formed over the first portion of the N-well. The first region extends in a first direction. The second region includes a first portion of a P-well and a plurality of N-type transistors formed over the first portion of the P-well. The second region extends in the first direction. The third region includes a second portion of the P-well. The fourth region includes a second portion of the N-well. The first region and the second region are disposed between the third region and the fourth region.