A semiconductor imager comprises a first and a second region (41, 42) which have a conductivity type opposite to a substrate (21) and are reverse biassed relative to the substrate beneath photosensitive regions (22) of each row and a reading device (26, 33) for the row, respectively, to be completely and not to be completely depleted, respectively. The imager may or may not comprise such a covering region (77) on each photosensitive region as may have the conductivity type of the first and the second regions and be not completely depleted. It is possible to provide a line sensor or a photodiode of a similar structure. Preferably, the first and the second regions have a common impurity concentration lower than the photosensitive regions and are respectively thinner and thicker relative to each other. The covering region preferably has the impurity concentration of each channel stopper (23).