An image sensor including a substrate having a first, a first device isolation region adjacent to the first surface and defining a unit pixel, a transfer gate on the first surface at an edge of the unit pixel, a photoelectric conversion part in the substrate and adjacent to a first side surface of the transfer gate, and a floating diffusion region in the substrate and adjacent to a second side surface of the transfer gate. The second side surface faces the first side surface. The first device isolation region is spaced apart from the second side surface. The substrate and the first device isolation region are doped with impurities having a first conductivity. A first impurity concentration of the first device isolation region is greater than a second impurity concentration of the substrate.