A simple analysis based on the bulk valence and conduction densities of states was employed to estimate the interface-state densities for interfaces between the three most common SiC polytypes (3C, 4H, and 6H) and SiO2. We found that all polytypes had comparable conduction-band interface-state density with silicon dioxide as Si, being higher for the valence band. The conduction-band interface-state density should be higher for 4H-SiC than for 6H-SiC for both the C- or Si-terminated interfaces. On the contrary, the valence-band interface-state density can be either higher or lower for 4H-SiC compared to 6H-SiC according to which atom, C or Si, terminates the interface. The trends suggested by the above model are in agreement with recent mobility measurements in SiC-based field-effect transistors. (C) 2001 American Institute of Physics.