Abstract: PN junction is the foundation of semiconductor device structure. And the measurement of doping distribution in PN junction directly relates to the performance and reliability of devices. For doping analysis, secondary electron image shows great potential. Based on scanning electron microscopy, the doping profiles of the PN junction in silicon-based MOSFETs and silicon carbide MOSFETs were measured, revealing significant differences in doping profiles between silicon and silicon carbide materials. To elucidate the underlying mechanisms of the observed discrepancies, the secondary electron emission coefficients of the pertinent materials were determined employing the sample current method. The analysis of the obtained results indicates that the variations in the secondary electron emission are associated with surface states, which holds significant implications for the application of secondary electron imaging in semiconductor measurements.