A new process for the fabrication of double positioning boundary (DPB) free 3C-SiC was demonstrated by utilizing the threading screw dislocations of 6H-SiC, using the following two steps: (1) formation of a spiral structure with six bilayer steps on a seed 6H-SiC; and (2) nucleation of 3C-SiC on the seed. In the first step, the six-bilayer step structure was formed via spiral dissolution using a molten Fe-Si alloy. The formation of a spiral structure on both the 6H-SiC (0001) and (0001¯) faces could be explained by BCF theory. In the second step, we observed that the nucleation and growth of 3C-SiC occurred only on the 6H-SiC (0001) face, while step-flow growth of 6H-SiC was observed on the (0001¯) face. The different growth modes presumably arose from the smaller step energy at the 6H-SiC (0001)/alloy interface than that at 6H-SiC (0001¯)/alloy interface, which was predicted from the width of the steps fabricated by the spiral dissolution. The obtained 3C-SiC on the continuous spiral steps of the seed 6H-SiC substrate had the same stacking structure as the seed, even at the 6H-SiC/3C-SiC interface. Consequently, we successfully obtained a DPB-free region of 3C-SiC from the start of the growth.