Additions of AlN and Al2O3 to beta-SiC hot pressed at 2100 degrees C strongly effect the beta- to alpha-SiC phase transformation and the resultant alpha-SiC polytypes which are formed. Scanning and transmission electron microscopy were utilized to investigate the microstructural changes occurring in SiC due to these additions and to correlate these observations to their mechanical properties. The results suggest that Al2O3 additions stabilize the formation of the 6H-polytype of alpha-SiC which grows rapidly into an elongated plate-like morphology, while AlN additions stabilize the 2H-polytype of alpha-SiC resulting in fine equiaxed 2H-SiC: AlN solid solution grains. It is speculated that the elongated growth of 6H-SiC with Al2O3 additions can be controlled through the simultaneous addition of AlN. The formation of 2H-SiC : AlN solid solution grains inhibits the growth of the 6H-SiC grains since AlN(2H) will not go into solid solution in the SiC(6H) structure, effectively pinning the growth of the 6H-SiC grains.