An image sensor may include: a photoelectric conversion element including a second conductive layer formed over a first conductive layer; an insulating layer and a third conductive layer which are sequentially formed over the second conductive layer; an opening exposing the second conductive layer through the third conductive layer and the insulating layer; a channel layer formed along the surface of the opening, and including first and second channel layers which are coupled to each other while having different conductivity types; and a transfer gate formed over the channel layer to fill the opening, and partially formed over the third conductive layer.