The shapes of the dangling-bond occupied-state band of various clean Si(001) surfaces are deduced from high-resolution photo-emission yield spectra. These are analyzed in terms of three components, respectively 0. 2, 0. 45 and 0. 75 ev below the valence band edge. The variations when the sample undergoes vacuum annealing or an oxidation-deoxidation cycle of the (001) and vicinal faces are correlated with the smoothing our roughening of the surface on the atomic scale. The ionization energy is found to be 5. 30 plus or minus 0. 05 ev whatever the surface roughness.