Embodiments relate to an image sensor and a method of forming an image sensor. According to embodiments, an image sensor may include a first substrate and a photodiode. A circuitry including a metal interconnection may be formed on and/or over the first substrate. The photodiode may be formed over a first substrate, and may contact the metal interconnection. The circuitry of the first substrate may include a first transistor, a second transistor, an electrical junction region, and a first conduction type region. The first and second transistors may be formed over the first substrate. According to embodiments, an electrical junction region may be formed between the first transistor and the second transistor. The first conduction type region may be formed at one side of the second transistor, and may be connected to the metal interconnection.