PURPOSE: To provide an electromagnetic wave sensor by which image sensing can be performed by easily detecting an electromagnetic wave such as visible radiation, infrared rays, ultraviolet rays, an X-ray, a (γ) ray or a millimeter wave while being an extremely simple structure.

CONSTITUTION: A functional substance 4 sensitive to an electromagnetic wave 3 is arranged on one surface of a semi conductor substrate 2 showing a diode characteristic, and a surface electrode 6 is arranged on an upper surface of this functional substance 4, and in a condition where DC voltage is impressed on this surface electrode 6, an electromagnetic wave 10 for a probe is irradiated to a depletion layer 2a of the semiconductor substrate 2, and an electric signal correlative to the electromagnetic wave 3 incident on the functional substance 4 is taken out of an ohmic electrode 7 arranged on the semiconductor substrate 2.