An image sensor has a semiconductor substrate of a first conductivity type having a photo-detecting surface and a semiconductor region of a second conductivity type disposed under the photo-detecting surface and forming a junction with the semiconductor substrate. A dielectric body is provided in the semiconductor substrate beneath the junction so that a width of the dielectric body in a direction parallel to the photo-detecting surface does not extend beyond a width of the semiconductor region in the direction parallel to the photo-detecting surface. The dielectric body is polarized due to charges forming a depletion region generated by the semiconductor substrate and the semiconductor region. A width of the dielectric body is approximately equal to a width of an inner surface of the depletion in the direction parallel to the photo-detecting surface of the semiconductor substrate.