1. An image sensor, comprising: a substrate including a spaced apart photoelectric conversion region and floating diffusion region therein, the photoelectric conversion region and the floating diffusion region comprising a first conductivity type; a device isolation region comprising an insulating material layer in the substrate adjacent a boundary of the photoelectric conversion region; a first well region of a second conductivity type in the substrate extending between the boundary of the photoelectric conversion region and the device isolation region; and a second well region of the second conductivity type in the substrate adjacent the floating diffusion region, the second well region having a dopant concentration less than that of the first well region.