Abstract: An IC structure includes a first transistor, a dielectric layer, a plurality of semiconductor pillars, a plurality of semiconductor plugs, a semiconductor structure, and a second transistor. The first transistor is formed on a substrate. The dielectric layer is above the first transistor. The semiconductor pillars extend from the substrate into the dielectric layer. The semiconductor plugs extend from a top surface of the dielectric layer into the dielectric layer to the plurality of semiconductor pillars. The semiconductor structure is disposed over the top surface of the dielectric layer. The second transistor is formed on the semiconductor structure.