The electronic subband structure of periodically n-type -doped silicon is calculated self-consistently within the local-density approximation. Two types of energy levels are distinguished, one due to valleys transverse to the superlattice axis, and the other due to longitudinal valleys. Minibands, potential profiles, miniband occupancies, and Fermi-level positions are studied and their dependence on the spacing d between layers and the doping concentration ND is obtained. Pronounced changes with increasing ND and decreasing d are observed. For d>150, and 1013ND<1015 cm-2, the system behaves as a set of practically independent isolated -doped wells. Significant dispersion of the higher subbands takes place for d lower than 150. The transition from a multiple - doped-well behavior to a superlattice regime is observed for doping concentrations >2.0×1013 cm-2 and periods d<50. The twofold degeneracy of longitudinal levels and the fourfold degeneracy of transverse levels are removed by the many-valley coupling. The corresponding splitting energies are calculated.