X-ray diffraction was utilized to follow the transformation from beta-SiC (3C) to the various alpha-SiC polytypes in the presence of AlN and Al2O3 additives after hot pressing from 1700 to 2100 degrees C. The 2H- and 6H-polytypes of alpha-SiC were the predominate polytypes with additions of only AlN or Al2O3, respectively. The amount of 2H- and 6H-polytypes, and subsequently the microstructural morphology of the SiC materials, were found to be controlled by varying the amount of AlN and Al2O3. Improvements in fracture toughness to similar to 9 MPa-root m were achieved with flexural strengths ranging from 600 to 900 MPa. These results suggest that accurate control of the polytypic make-up of SiC-based materials, along with their mechanical properties, can be achieved through AlN and Al2O3 additions.