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In this paper, we review our research on 6H-SiC polytype inclusions in 3C-SiC layers, which were grown on nominally on-axis 6H-SiC substrates using sublimation epitaxy. More than 90% coverage by 3C-SiC is typically achieved at growth temperature of 1775 degrees C. The main reason for the polytype inclusions to appear is local supersaturation non-uniformities over the sample surface which appear due to the temperature gradient and spiral growth nature of 6H-SiC. On the 6H-SiC spirals with small steps supersaturation is smaller and 3C-SiC nucleation and growth is diminished. Due to surface free energy and surface diffusion differences, polytype inclusions appear differently when 3C-SiC is grown on the Si- and C-faces. The 6H-SiC inclusions as well as twin boundaries act as neutral scattering centers and lower charge carrier mobility