Two-dimensional scanning tunneling microscope measurements on cleaved interdigitated shallow pn-junctions are presented as an example of the potential of scanning tunneling microscopy in device and process analysis. The ultra-high vacuum instrumentation used for the measurements is also discussed. The two-dimensional part of the junction is localized to within 30 nm. The cleaving of the junctions and the measurements are performed in ultra-high vacuum. Measurements on pn-junctions in air are also discussed. These measurements show that there is a relation between the magnitude of the tunneling current and the local impurity concentration of the sample. A qualitative model is presented that explains the observed effects.