Energy dispersive X-ray microanalysis in the SEM has long been used as a tool to identify defects in semiconductors. Such defect analysis typically meant running the SEM at relatively high voltages, 10 – 20 kV. This technique was suitable for bulk analysis but starts to fail as semiconductor features and defects get smaller. In the current era of sub-micron and nano-scale devices, the key to high resolution analysis is to use very low accelerating voltages, typically below 5 kV, and to look at L and M X-ray lines. It is also useful to model samples in software to determine the best set of operating conditions to use for any given sample. This tutorial will demonstrate a Monte Carlo based software program, and show how it can be used to determine the best SEM and X-ray setting to use to obtain reliable sub-micron analysis results.