An image sensor includes a first semiconductor chip having a first surface and a second surface, the first semiconductor chip a including an array of unit pixels configured to capture light corresponding to an image and to generate image signals based on the captured light and a second semiconductor chip having a first surface and a second surface, the second semiconductor chip including first peripheral circuits configured to control the array of pixels and receive the generated image signals, the first peripheral circuits including a vertical scanning circuit, a horizontal scanning circuit, and a signal read-out circuit, the first semiconductor chip being stacked on the second semiconductor chip, the first semiconductor chip not being smaller than the second semiconductor chip.
