Scanning probe microscopy techniques such as conventional atomic force microscopy (AFM), electrostatic force microscopy (EFM) and scanning capacitance microscopy (SCM) have emerged as powerful tools for the nanoscale characterization of electronic materials and devices. These techniques have very high spatial resolution in both the lateral and vertical dimensions, and are relatively easy to use because measurements can be performed in air at room temperature. We have used cross-sectional scanning force microscopy to image a variety of group III-V and group IV semiconductor structures. The first part of the presentation will describe a study using a variation of cross-sectional EFM to characterize dopant distributions and layer thickness in MOCVD-grown AlxGa1-xAs/GaAs heterojunction bipolar transistor structures.  The second part of the talk will describe cross-sectional SCM studies of focused ion beam (FIB) As+-implanted p-type silicon to examine the in-depth and lateral spread of the activated free carriers. Several samples with varying implant conditions (energy, dose, and line width) and post-implant annealing conditions were examined. Preliminary analysis allows us to delineate the location of both the metallurgical and electrical p-n junction. The results are then compared with computer simulations that include the effects of implantation damage and rapid thermal treatment.