An in‐situ low‐energy electron diffraction (LEED) study has been made of the homoepitaxial growth in ultrahigh vacuum of silicon films up to several microns thickness. During growth on (111) at temperatures between 600 and 1000°C the initial Si(111)‐7 surface structure of the substrate is retained by the epitaxial film. Below 600°C a mixed Si(111)‐7 and Si(111)‐5 structure develops in the initial stages of growth and for a given temperature, is preserved as epitaxy proceeds. At temperatures lower than 350°C the LEED data indicate that the film structure becomes amorphous. Epitaxy on (100) occurs at temperatures down to about 300°C. In this case the initial Si(100)‐2 surface structure is retained by the film except in the range 650 to 700°C, where a new ordered form of the Si(100)‐2 structure is generated.