tAtomic-scale understanding and processing of the surface and interface properties of antimony trioxide(Sb2O3) are essential to the development of nanoscale Sb2O3materials for various applications, suchas photocatalysts, transparent conducting oxides, optical coatings, dielectric films, and fire retardants.Lack of atomically well-defined, crystalline Sb2O3templates has however hindered atomic resolutioncharacterization of the Sb2O3properties. We report the preparation of crystalline Sb2O3thin films on theSi(1 0 0) substrate with a simple process by oxidizing Sb-covered Si(1 0 0) in proper conditions. Physicalproperties of the synthesized films have been elucidated by low-energy electron diffraction, scanningtunneling microscopy and spectroscopy, and ab initio calculations. The spectroscopic results show thatthe band gap of Sb2O3is 3.6 eV around the gamma point (i.e. ). Calculations reveal energetically favoredSb2O3(1 0 0) surface structures. The findings open a new path for the atomic-scale research of Sb2O3.