[en] Self-consistent calculations of the energy bandstructure of YS using the augmented plane wave method and the Xα exchange potential are reported. The non-metal p/metal d interaction, discussed in terms of partial l-like charges, is found to be strongly reduced in YS compared with the isostructural and isoelectronic NbC. The S-K, S-Lsub(III), Y-Lsub(III), Y-Msub(III) and Y-Msub(v) x-ray emission spectra are calculated on the basis of the bandstructure results. The closely related Y-Lsub(III) and Y-Msub(III) spectra are predicted to be significantly different, owing to important matrix element effects. (author)