X-ray and electron diffraction have been used to study structure modifications in polysilicon films produced by low-pressure chemical vapour deposition. It was shown that additional diffraction reflections are observed in polysilicon films with fibrous and dendritic structure. These additional reflections may be considered as relative to close-packed hexagonal structure with the following lattice parameters: a = 3.808 Angstrom, b = 6.186 Angstrom. The orientation relationship between the cubic diamond and hexagonal phases is [1 1 1](cub) parallel to [0 0 1] and ((1) over bar 1 0)(cub)* parallel to (1 0 0)*. The suggested hexagonal structure formation mechanism is based upon the existence of planar faults in {1 1 1} planes.