An image sensor including a pixel assembly, each pixel including a photodiode and an access transistor connected to a read circuit, the photodiode and the access transistor being formed in and above a first semiconductor substrate, all or part of the read circuit being formed in a second semiconductor substrate, the second substrate being placed above the first substrate and separated therefrom by an intermediary insulating layer covering the access transistor, the photodiode receiving incident photons on its lower surface side opposite to the intermediary insulating layer.