Crystal mosaicity of SiC crystals grown by the physical vapor transport (PVT) method has been investigated. High resolution x-ray diffractometry (HRXRD) measurements were performed to investigate the evolution of crystal mosaicity during growth of SiC. 4H-SiC crystals were grown in the [000 (1) over bar] and [11 (2) over bar0] directions, and sliced wafers from these crystals having various surface orientations were examined. For the [000 (1) over bar] grown crystals, the crystal mosaicity resulted from foreign polytype inclusions, while for the [11 (2) over bar0] growth, a drastic change in the mosaic structure between the seed and the grown crystals was observed. The mosaicity became well evolved quite soon after polytype instabilities occurred, which suggests that rearrangement motions (glide and climb motions) of dislocations introduced by polytype instabilities are highly activated processes during PVT growth of SiC.