Solid state phase transitions in SiC are investigated using diuse X-ray scattering and Monte Carlo simulations. As an example, the 3C-6H transformation is investigated in details. The transformation is modeled with a statistical algorithm based on the concept of double cross-slipping and subsequent dissociation of basal plane dislocations. The corresponding diuse X-ray scattering curves are calculated and quantitatively compared with experimental data obtained from 3C-SiC crystals annealed at high temperatures (1700-2100 • C). From the simulations, it is demonstrated that the transformation implies the multiplication and ordering of double and triple stacking faults (SFs). The transformation level and root-mean-squared strains associated with the dislocations could be determined from the simulations. The defect structure formed during the transition can be rationalized by considering the relative energies of the SFs. Using an axial next-nearest neighbor Ising interaction model we show that single SFs are not energetically favored, whereas the simultaneous occurrence of double and triple SFs implies their relative energy dierence to remain below a critical value (∼ 8-9%).