Highly oriented large‐area silicon films have been deposited onto single crystal Si, ‘111’ substrates. Illumination of the substrates with a mercury vapor lamp during deposition appeared to be essential for obtaining oriented films. The deposition was accomplished by an H2 reduction of . The energy of activation for this reaction was found to be 35.7 kcal/mole ± 5%. Utmost chemical cleanliness of the substrate surface is essential and more critical than for high temperature deposition.