Improved process control, lowered costs and reduced risks can be realized through the use of non-destructive mobility and sheet charge density measurements during the fabrication of GaAs and GaN wafers. The results from this microwave-based technique are shown to agree with destructive van der Pauw Hall testing results to within +/-5%. In addition, it has the ability to map wafer uniformity and provide separated 2DEG data for thick cap or multi-layered structures. As a result, this technique provides an efficient and cost-effective alternative to current process control metrology methods, while providing the user with important process control data. (C) 2004 Published by Elsevier B.V.