Provided is an image sensor that comprises a readout circuitry, an interlayer dielectric, an interconnection, an image sensing device, an ion implantation region, a contact, and a pixel separation layer. The readout circuitry is disposed at a first substrate. The interlayer dielectric is disposed on the first substrate. The interconnection is disposed in the interlayer dielectric, and electrically connected to the readout circuitry. The image sensing device is disposed on the interconnection, and comprises a first conductive type layer and a second conductive type layer. The contact electrically connects the first conductive type layer of the image sensing device and the interconnection. The ion implantation region is formed in the second conductive type layer at a region corresponding to the contact. The pixel separation layer is disposed at a pixel boundary of the image sensing device.