A semiconductor energy detector, comprising: a semiconductor substrate comprised of a semiconductor of a first conductivity type, onto which an energy ray of a predetermined wavelength range is incident from an incident surface thereof; wherein a diffusion layer of a second conductivity type (4,5) comprised of a semiconductor of a second conductivity type and a diffusion layer of the first conductivity type comprised of a semiconductor of the first conductivity type higher in impurity concentration than said semiconductor substrate, are provided on a surface opposite to the incident surface of said semiconductor substrate; a plurality of said diffusion layers of the second conductivity type (4,5) are arrayed at a predetermined interval; wherein said first diffusion layer of the first conductivity type for separating said diffusion layers of the second conductivity type (4,5) is provided between said diffusion layers of the second conductivity type (4,5), said first diffusion layer of the first conductivity type comprising a higher impurity concentration than said semiconductor substrate; wherein a second diffusion layer of the first conductivity type is provided on an outside of an array of said diffusion layers of the second conductivity type (4,5), said second diffusion layer of the first conductivity type comprising a higher impurity concentration than said semiconductor substrate, characterized in that said second diffusion layer of the first conductivity type is provided on a surface opposite to the incident surface of said semiconductor substrate; wherein said first and second diffusion layer of the first conductivity type (6,7) are electrically connected to each other; wherein said second diffusion layer of the first conductivity type is formed to be wider than said first diffusion layer of the first conductivity type; and wherein all said diffusion layers (4,5,6,7) are arranged laterally on the surface opposite to the incident surface of said semiconductor substrate. a semiconductor substrate comprised of a semiconductor of a first conductivity type, onto which an energy ray of a predetermined wavelength range is incident from an incident surface thereof; wherein a diffusion layer of a second conductivity type (4,5) comprised of a semiconductor of a second conductivity type and a diffusion layer of the first conductivity type comprised of a semiconductor of the first conductivity type higher in impurity concentration than said semiconductor substrate, are provided on a surface opposite to the incident surface of said semiconductor substrate; a plurality of said diffusion layers of the second conductivity type (4,5) are arrayed at a predetermined interval; wherein said first diffusion layer of the first conductivity type for separating said diffusion layers of the second conductivity type (4,5) is provided between said diffusion layers of the second conductivity type (4,5), said first diffusion layer of the first conductivity type comprising a higher impurity concentration than said semiconductor substrate; wherein a second diffusion layer of the first conductivity type is provided on an outside of an array of said diffusion layers of the second conductivity type (4,5), said second diffusion layer of the first conductivity type comprising a higher impurity concentration than said semiconductor substrate, characterized in that said second diffusion layer of the first conductivity type is provided on a surface opposite to the incident surface of said semiconductor substrate; wherein said first and second diffusion layer of the first conductivity type (6,7) are electrically connected to each other; wherein said second diffusion layer of the first conductivity type is formed to be wider than said first diffusion layer of the first conductivity type; and wherein all said diffusion layers (4,5,6,7) are arranged laterally on the surface opposite to the incident surface of said semiconductor substrate.