An image sensor and an electronic device are disclosed. At least one pixel in the image sensor includes a photodiode, a floating diffusion region and a transfer transistor located between the photodiode and the floating diffusion region. The photodiode includes a carrier-accumulation region, and a gate of the transfer transistor extends up to the carrier-accumulation region. The gate extends away from the floating diffusion region and overlaps over half of a width of the carrier-accumulation region. Since carriers move at a higher speed in a fast transfer channel in the semiconductor substrate around such a gate, increasing the length of the transfer transistor's gate extending away from the floating diffusion region and overlapping range with the carrier-accumulation region can facilitate fast movement of carriers from the carrier-accumulation region through such fast transfer channels to the floating diffusion region, thereby improving overall carrier transfer efficiency and optimizing performance thereof.