We report the epitaxial growth of (100)- and (1 1 1)-oriented CeSb thin films on Al2O3 (1 1 2 0) and (0 0 0 1) substrates by means of molecular beam epitaxy. Depending on the overall Sb-to-Ce flux ratio and the molecular state of Sb,,, we observe a re-entrance behavior in the phase formation and orientation of CeSb on Al2O3 (1 1 2 0). This behavior is shown to exhibit, in some respect, similarities to III-V compound growth, but also more complexities due to the instability of the rare earth component against oxidation. A geometric orientation selection model is suggested which reproduces the observed re-entrance behavior as well as the overall CeSb growth rate.