A method is provided for measuring electrical potentials at solid state matter wherein an ionizing radiation is directed against a measuring point at the surface, whereby a conductive connection between the measuring point at the surface and a measuring point at the solid state matter is produced, its electrical potential to be measured. Electrical potentials are measured at a solid state substance even when the solid state matter is hidden beneath at least one conductive layer and at least one insulating layer. The electrical potential at the solid state matter is identified by measuring induced specimen current.