The effects of process variables on the growth rate and properties of insulating films grown from a hydrogen‐silane‐ammonia mixture have been studied. Growth rate vs. 1/T is observed to have a break at 900°C, coincident with an observed amorphous‐polycrystalline transition. Hardness, growth rate, and refractive index are found to move toward values appropriate for silicon as the per cent ammonia is reduced. The thermal expansion coefficient can be varied from approximately that of silicon to appreciably more by increasing the per cent ammonia. A variety of other properties, such as breaking strength and Youngs' modulus were also measured and are discussed.