29Si magic-angle-spinning nuclear-magnetic resonance has been measured on spinel-type cubic silicon nitride (c-Si3N4). c-Si3N4 shows two 29Si resonances at -50.0±0.2 and -225.0±0.2 ppm, corresponding to the tetrahedron SN4 and the octahedron SiN6, respectively. Integration of the spectrum gives SN4/SiN6 about one half that of the spinel structure. Ab initio self-consistent field Hartree–Fock molecular orbital calculations also indicate that the chemical shift for octahedral Si is more negative in nitride than in oxides. © 2001 American Institute of Physics.