A novel non-destructive method to characterize stacking faults (SF) in 3C-SiC crystals is presented. This method is based on fast X-ray diffraction reciprocal space mapping and can be used qualitatively for routine analysis of 3C-SiC as SFs give rise to a characteristic star-like pattern in reciprocal space whose intensity depends on the SF density. The simulation of the diffusely scattered intensity streaks with an appropriate model enables one to also obtain quantitative results such as SF densities, mosaic domain size and mosaicity. The model is tested with a commercial (001) 3C-SiC crystal from HAST corporation, and then it is used to analyse SFs in (111) 3C-SiC crystals grown by continuous feed-physical vapour transport. 1