High-resolution electron microscopy and matching simulations were used to investigate structural features of a GaN/SiC heterointerface. The polarity of the (0001)-oriented SiC substrate was confirmed and it was shown that the polarity of the GaN epilayer corresponded to Ga-terminated (0001) growth. From measurement of average (1100) rather than (000l) interplanar spacings it was established that the GaN/SiC interface was abrupt to within one atomic plane. It was concluded that the atomic arrangements at the GaN/SiC interface most likely consisted of N bonded with Si, but with some Ga bonded to C in order to maintain charge balance. © 2000 American Institute of Physics.