The development of 3C-SiC crystals from <0001> oriented hexagonal seed has always suffered from the systematic twinning which appears during the nucleation step of the layer. Using the continuous feed – Physical Vapour Transport (CF-PVT) growth process, we succeeded in growing single domain 3C-SiC crystals. To explain that, we propose in this work, a model based on the interaction between the lateral expansion anisotropy of 3C-SiC nuclei and the step flow growth front. Depending on the step edges direction, we can obtain one 3C orientation developing simultaneously with the vanishing of the other one. This model is confirmed by cross sectional HRTEM observation of the α-β interface.