Abstract: The present invention relates to a method for determining characteristic electrical properties of semi-conducting materials wherein the time/frequency dependent electrical impedance or admittance of the material is measured. The invention also relates to an apparatus for carrying out the method. A number of bulb and surface parameters characterize the electrical properties of a given piece of material. These parameters include the dielectric constant .epsilon. of the material, the difference .DELTA..mu..sub.ch in the chemical potential of the bulk of a material and the chemical potential of its surface and/or metal electrode--material surface interface, the density of the majority and minority electrical mobile charge carriers N and N.sub.min, respectively, in the bulk of the material, the electrical mobility .mu. of the majority electrical mobile charges in the bulk of the material and the electrical mobility .mu..sub.min of minority mobile charge carriers, the surface and bulk emission and capture rates E.