We study several semiconductor defects at the 4H-SiC(0 0 0 1)/SiO2 interface within a spin-polarized generalized-gradient density-functional approach for identifying candidate defects responsible for the high density of interface defects measured in the upper part of the 4H-SiC band gap. Using a model structure of the 4H-SiC(0 0 0 1)/SiO2 interface, we determine the energy levels of several defects with respect to the SiC band edges and identify the carbon interstitial as a possible candidate. (c) 2007 Elsevier B.V. All rights reserved.