In this work, we used time-of-flight (ToF)-SIMS spectrometry to study the structure and chemical composition of the interface region of Al contacts to n-type 4H silicon carbide (SiC). The obtained ToF-SIMS depth profiles showed that the annealing of the Al/4H-SiC contacts in the temperature range of 700 °C–1000 °C results in reaction between Al and SiC, and products of this reaction, crystalline silicon and aluminum carbide (Al4C3), are accumulated in the contact layer. In addition, recorded ToF-SIMS images demonstrated that the annealing of the contact results in inhomogeneous chemical composition of its interface region. It was shown that the thermally induced modification of structure and the composition of the contact interface affect its I–V characteristic. The formation of Al contact to crystalline Si was proposed as the main factor responsible for the observed changes of I–V characteristic of Al/SiC contacts upon annealing. Copyright © 2012 John Wiley & Sons, Ltd.