A thin microcrystalline silicon semiconductor film suitable for use as an intrinsic semiconductor layer in an amorphous silicon solar cell or the like comprises an amorphous phase with crystallites contained therein in the form of a prismatic or conical crystallite aggregate phase. Additional crystallites may be dispersed as individual crystallites in the amorphous phase. In the thin film, the crystalline fraction may preferably range from 5 to 80% and the crystallite size may preferably range from 2 to 1,000 nm. This thin film can be formed by first forming an initial film to a thickness in a range of from 2 nm to 100 nm at a deposition rate of from 0.01 nm/sec to 0.1 nm/sec on a substrate and then forming a principal film at a deposition rate of from 0.1 nm/sec to 2 nm/sec, for example, in accordance with RF plasma CVD.
