Embodiments relate to an image sensor. According to embodiments, an image sensor may include a metal interconnection, readout circuitry, a first substrate, a metal layer, and an image sensing device. The metal interconnection and the readout circuitry may be formed on and/or over the first substrate. The image sensing device may include a first conduction type conduction layer and a second conduction type conduction layer and may be electrically connected to the metal layer. According to embodiments, an electric field may not be generated on and/or over an Si surface. This may contribute to a reduction in a dark current of a 3D integrated CMOS image sensor.