Films of antimony were deposited by evaporation on interchangeable emitters in concentric-sphere, retarding-potential phototubes. Below thicknesses of about 300 A, they behaved as semiconductors. The Fermi level lay about 0.1 ev above the occupied band. They converted irreversibly to the normal crystalline metallic form at 200\ifmmode^\circ\else\textdegree\fi{}C or somewhat higher. The results are consistent with previous measurements on the electrical resistance and optical transmission of thin antimony films; they indicate that the semiconducting form is amorphous. Analogies with the behavior of arsenic are mentioned.