An image sensor includes a first substrate including a driving element, a first insulation layer on the first substrate and on the driving element, a second substrate including a photoelectric conversion element, and a second insulation layer on the second substrate and on the photoelectric conversion element. A surface of the second insulation layer is on an upper surface of the first insulation layer. The image sensor includes a conductive connector penetrating the second insulation layer and a portion of the first insulation layer. Methods of forming image sensors are also disclosed.