Disclosed are semiconductor structures and methods of forming them. The structures include field effect transistors (FETs) with different type conductivities in different levels, respectively, of the same fin, wherein the numbers of FETs in the different levels are different. Specifically, in a fin, a first semiconductor layer has source/drain and channel regions for a first and a second transistor and a second semiconductor layer has source/drain and channel regions for a third transistor with a different type conductivity than first and second transistors. A gate is on the top surface and sides of the first semiconductor layer at the channel region of the first transistor. Another gate has a lower portion on the sides of the first semiconductor layer at the channel region of the second transistor and an upper portion on the top surface and sides of the second semiconductor layer at the channel region of the third transistor.