Each pixel of a global shutter back-side illuminated image sensor includes a photosensitive area. On a front surface, a first transistor includes a vertical ring-shaped electrode penetrating into the photosensitive area and laterally delimiting a memory area. The memory area penetrates into the photosensitive area less deeply than the insulated vertical ring-shaped electrode. A read area is formed in an intermediate area which is formed in the memory area. The memory area, the intermediate area and read area define a second transistor having an insulated horizontal electrode forming a gate of the second transistor. The memory area may be formed by a first and second memory areas and an output signal is generated indicative of a difference between charge stored in the first memory area and charge stored in the second memory area after a charge transfer to the first memory area.