An image sensor may include: a photoelectric conversion element suitable for generating a photo charge in response to incident light; and a transfer transistor suitable for transferring the photo charge generated by the photoelectric conversion element to a floating diffusion in response to a transfer signal, the transfer transistor comprising a first transfer gate formed over the photoelectric conversion element; an opening formed in the first transfer gate and exposing the photoelectric conversion element; a second transfer gate formed in the opening; and a channel layer interposed between the first and second transfer gates and between the photoelectric conversion element and the second transfer gate.