A photo detector and related fabricating method are disclosed. The photo detector includes a substrate, a first patterned semiconductor layer, a dielectric layer, a patterned conductive layer, an inter-layer dielectric, a second patterned semiconductor layer, two first electrodes disposed on the inter-layer dielectric and two second electrodes disposed on portions of the second semiconductor layer. The first patterned semiconductor layer having a first doping region and a second doping region is disposed on a transistor region. The dielectric layer is disposed to cover the substrate and the first semiconductor layer. The patterned conductive layer is disposed on the dielectric layer. The inter-layer dielectric having at least two openings adapted to expose the first doping region and the second doping region is disposed to cover the dielectric layer. The second patterned semiconductor layer is disposed on a photosensitive region. The first electrodes are electrically connected to the first patterned semiconductor layer.