A layout structure includes a substrate, a well, a first dopant area, a second dopant area, a first poly region, a third dopant area, a fourth dopant area, and a second poly region. The well is in the substrate. The first poly region is in between the first dopant area and the second dopant area. The second poly region is in between the third dopant area and the fourth dopant area. The first dopant area, the second dopant area, the third dopant area, and the fourth dopant area are in the well. The first dopant area is configured to serve as a source of a transistor and to receive a first voltage value from a first power supply source. The well is configured to serve as a bulk of the transistor and to receive a second voltage value from a second power supply source.