We use curved-space polytope lattices to model the defect-free regions of amorphous semiconductors. A particular structural feature, a channeling axis associated with a local screw symmetry, is suggested by the polytope model and can be found in previous amorphous network models. Its presence implies electronic eigenstates with phase coherence over many bond lengths. We present a "band structure" for amorphous Si based on this coherence. © 1984 The American Physical Society.