Using a self-consistent linear combination of atomic orbitals method based on density-functional theory in a local-density approximation, the electronic structure in the high-temperature ceramics ␣-Si 3 N 4 and ␤-Si 3 N 4 and at the Si͑111͒/Si 3 N 4 ͑001͒ interface have been calculated. The resulting charge transfer suggests that the ionic formula can be written as Si 3 ϩ1.24 N 4 Ϫ0.93 . For the Si͑111͒/Si 3 N 4 ͑001͒ interface, the silicon atoms from the silicon side lose some electrons to the nitrogen atoms of the silicon nitride side forming Si-N bonds at the interface. The calculated electronic density of states spectrum of Si 2 p core levels for this interface is in good agreement with x-ray photoemission spectroscopy experiments. ͓S0163-1829͑98͒06928-8͔