A 3D vertically integrated FET for CMOS cell circuits is disclosed. Vertically integrating FETs for a 3D cell circuit reduces the footprint size of an IC chip. To reduce a CMOS cell circuit footprint, a PFET and an NFET are vertically integrated by stacking a second semiconductor layer including a second FET above a first semiconductor layer including a first FET, such that the channel structure of the second FET overlaps the channel structure of the first FET. The first FET may be an NFET, and the second FET may be a PFET, or vice versa. The longitudinal axis of the first FET channel structure may extend in a first plane parallel to a second plane including the longitudinal axis of the second FET channel structure. The longitudinal axes may be parallel or at an angle to each other, such that the second channel structure overlaps the first channel structure.