Despite the rapidly increasing capabilities of Poisson deconvolution schemes for spreading resistance (SR) measurements, carrier spilling effects will remain a serious problem for the interpretation of SR profiles for structures involving significant forward spilling such as epilayers. In order to remedy this situation a spreading impedance probe is being developed allowing to influence the internal spilling by an external dc field, while performing an impedance measurement at a small ac bias. Three-dimensional calibration surfaces representing resistance versus resistivity and dc bias determine the probe characteristics. Results for a p well and a p . p+ epilayer will be discussed.