Electric field sensitive scanning probe microscopes (SPMs) can image the electronic properties of a semiconductor through an insulating layer-making the techniques well suited to extract underlying substrate dopant densities. A standard atomic force microscope (AFM) can be used to sense electric field by measuring the electrostatic response of a vibrating cantilever. We have constructed an inexpensive accessory to a commercial AFM to simultaneously acquire images of the spatial variations in substrate doping along with accurate topographic images. Our electric field images have a spatial resolution of 1 mum. In addition, we show explicitly how a simple parallel plate model can be used to extract the magnitude of lateral changes in dopant density from the electric field images. For a substrate doping density of 1 x 10(16) cm(-3) we can discern resistivity changes of similar to1 Omega cm. (C) 2002 Elsevier Science B.V. All rights reserved.