a solid state image sensor includes a semiconductor substrate of a first conductivity type , in a plurality of cell units formed in the surface region of the semiconductor substrate . each of the cell units includes a photo detector portion and an electric charge reading portion . the photo detector portion includes a first impurity region of a second conductivity type formed in the surface region of the semiconductor substrate and a second impurity diffusion region of the first conductivity type formed in the surface region of the first impurity region . the electric charge reading portion includes a third impurity region of the second conductivity type formed in the surface of the semiconductor substrate , a first insulation film formed on the third impurity diffusion region and an electrode formed in the first insulation film .