A unit pixel of a stacked image sensor includes a stacked photoelectric conversion unit, a first and second signal generating units. The stacked photoelectric conversion unit includes first, second and third photoelectric conversion elements that are stacked on each other. The first, second and third photoelectric conversion elements collect first, second and third photocharges based on first, second and third components of incident light. The first signal generating unit generates a first pixel signal based on the first photocharges and a first signal node and generates a second pixel signal based on the second photocharges and the first signal node. The second signal generating unit generates a third pixel signal based on the third photocharges and a second signal node. At least a portion of the second signal generating unit is shared by the first signal generating unit.