An integrated circuit includes a first transistor, a second transistor, a first power line, and a second power line. The first transistor has a first active region and a first gate structure, in which the first active region has a source region and a drain region on opposite sides of the first gate structure. The second transistor is below the first transistor, and has a second active region and a second gate structure, in which the second active region has a source region and a drain region on opposite sides of the second gate structure. The first power line is above the first transistor, in which the first power line is electrically connected to the source region of first active region. The second power line is below the second transistor, in which the second power line is electrically connected to the source region of second active region.