An image sensor may include: a substrate including a photoelectric conversion element; a first interlayer dielectric layer formed over the photoelectric conversion element; a channel layer including a first region and a second region, the first region being formed in an opening passing through the first interlayer dielectric layer, with a portion of the first region contacting the photoelectric conversion element, and the second region being formed over the first interlayer dielectric layer; a transfer transistor formed over the first region of the channel layer, the transfer transistor including a transfer gate which gapfills the opening; and a reset transistor including a reset gate formed over the second region of the channel layer.