An image sensor includes: a light receiving section suitable for generating photocharges in response to incident light; and a driving section including a source follower transistor suitable for generating an output voltage corresponding to a reference voltage in response to the photocharges. The source follower transistor includes: a stack structure formed by sequentially stacking a first conductive layer, an insulating layer and a second conductive layer; an open portion formed through the second conductive layer and the insulating layer so as to expose the first conductive layer; a channel layer formed along the surface of the open portion so as to be connected to the first conductive layer and the second conductive layer; and a gate is connected to the light receiving section and which is formed over the channel layer so as to overlap the second conductive layer.