A method for fabricating a photo diode first involves providing a substrate. A doping area is then formed on the substrate. Afterwards, a dielectric layer, and a first poly-silicon layer are formed on the substrate. An opening is then formed to expose a surface of the doping area. A second poly-silicon layer is formed on the first poly-silicon layer and within the opening. The second poly-silicon layer is patterned to form a wire, while the first poly-silicon layer is patterned to form a gate. Finally, a source/drain is formed.