The paper presents an experimental study aiming to highlight the potential of scanning microwave microscopy (SMM) as a non-destructive high precision characterization tool for SOI technology. Two identical SOI wafers having passivated and non-passivated top Si film surfaces have been assessed. Differential microwave measurements were found capable of detecting differences in the structures of the two samples. The results support the conclusion that, after appropriate calibration method, SMM may provide a powerful tool offering nm scale characterization for SOI technology.