After a gate oxide film 10 has been formed on a silicon substrate G, a first step of forming a microcrystalline silicon film by high electron density plasma of an electron temperature of 2.0 eV or less and a second step of forming an ultra-microcrystalline silicon film by high electron density plasma of an electron temperature higher than 2.0 eV are repeated. A stacked-layer film 20 of the ultra-microcrystalline silicon film and the microcrystalline silicon film is thereby formed. With the film formation method described above, at least one of an n-channel thin-film transistor and a p-channel thin-film transistor with the stacked-layer film 20 functioned as an active layer may be manufactured.