A 10 nm thick Ho film was deposited on a Si(100) 2 x 1 surface at room temperature. Epitaxial HoSi2 layer was formed by solid phase reaction at different temperatures. The epitaxial growth was monitored in situ by LEED and the as-grown film was investigated by X-ray Diffraction (XRD), TEM and Rutherford Backscattering (RBS) and channeling. At 500 degrees C a Si-Ho reaction was detected without any epitaxial character. Further annealing at 700 degrees C produced a clear, though not very sharp, LEED pattern. XRD showed clear epitaxial HoSi2 with a relatively large peak width. Electron diffraction confirmed the epitaxial film but RES channeling showed no reduction of the Ho signal. These observations could be explained partly by strained epitaxy and maybe by the existence of epitaxial grains misoriented with less than or equal to 1.0 degrees or twin crystals.