Amorphous silicon films, prepared by planar rf magnetron sputtering, in both hydrogenated and unhydrogenated forms, are found to exhibit three distinct types of microstructure depending on the growth conditions: (a) no resolvable microstructure down to 10 A˚; (b) islands of 50–200 A˚ lateral dimensions separated by a network of lower density; (c) a two level pattern wherein conglomerates of 50–200 A˚ islands form columnar regions of 300–500 A˚ lateral dimensions interspersed by a more pronounced low density network. The argon pressure during growth has the dominant influence on the evolution of the microstructure. Type (a) microstructure is obtained at low (≤ 3 mTorr) argon partial pressure irrespective of rf power level, hydrogen partial pressure, and substrate temperature and type (b) and (c) microstructures are observed at higher argon partial pressures (≥10 mTorr). Increasing rf power and substrate temperature at high argon partial pressures result in an enhancement of the microstructural features. Addition of hydrogen enhances the microstructure at low rf power levels and suppresses the microstructure at high rf power levels.