With an innovative measurement technique termed “microwave detected photoconductivity” (MDP) it is possible to investigate defects of silicon wafers contact less and topographically by evaluating photoconductivity transients detected via microwave absorption. Thus it is possible to obtain the electrical key parameters (e.g. diffusion length and lifetime) in a contact less, non destructive and topographic way. The method is ideal for the investigation of process induced defects as a function of different processing steps. The inhomogeneities of the diffusion length map of the pure wafer correlate very well with the key parameter map of photosensor devices. Even more details of process induced failures of devices can be detected in detail with MDP. In general, the measurement conditions together with their evaluation can be tuned to nearly ‘predict’ properties and production yield of final devices for a given chain of processing steps.