In a radiation detector, a Schottky electrode is formed such that an interdiffusion coefficient between the material of an outermost surface electrode formed on the Schottky electrode and the material of the Schottky electrode is smaller than an interdiffusion coefficient between the material of the outermost surface electrode and Al (aluminum). Consequently, the material of the outermost surface electrode does not diffuse into the Schottky electrode, and Schottky functions can be maintained, and at the same time, the material of the Schottky electrode does not diffuse into the outermost surface electrode, and the outermost surface electrode can be prevented from alloying.