A semiconductor image sensor includes a plurality of pixels. Each pixel of the sensor includes a semiconductor substrate having opposite front and back sides and laterally delimited by a first insulating wall including a first conductive core insulated from the substrate, electron-hole pairs being capable of forming in the substrate due to a back-side illumination. A circuit is configured to maintain, during a first phase in a first operating mode, the first conductive core at a first potential and to maintain, during at least a portion of the first phase in a second operating mode, the first conductive core at a second potential different from the first potential.