An image sensor includes a semiconductor substrate having a pixel region and a peripheral circuit region. An interlayer dielectric layer has metal wirings and a pad formed over the semiconductor substrate. A lower electrode is selectively formed over the metal wirings. A photo diode is formed over the interlayer dielectric layer of the pixel region. An upper electrode formed over the photo diode. Therefore, a vertical integration of the transistor and the photodiode may approach a fill factor to 100%, and provide higher sensitivity, implement more complicated circuitry without reducing sensitivity in each unit pixel, improve the reliability of the image sensor by preventing crosstalk, etc., between the pixels, and improve light sensitivity by increasing the surface area of the photo diode in the unit pixel.