Abstract: An image sensor structure and methods of forming the same are provided. An image sensor structure according to the present disclosure includes a semiconductor substrate including a photodiode, a transfer gate transistor disposed over the semiconductor substrate and having a first channel area, a first dielectric layer disposed over the semiconductor substrate, a semiconductor layer disposed over the first dielectric layer, a source follower transistor disposed over the semiconductor layer and having a second channel area, a row select transistor disposed over the semiconductor layer and having a third channel area, and a reset transistor disposed over the semiconductor layer and having a fourth channel area. The second channel area is greater than the first channel area, the third channel area or the fourth channel area.