Boron surface segregation in Si molecular beam epitaxy has been measured on Si(111) substrate as a function of the growth temperature (400 °C≤Ts≤900 °C) by Auger electron spectroscopy. Boron oxide (B2O3) was used as dopant material to achieve a boron concentration level of about 1×1019 cm−3. Three temperature regions are observed for the behavior of the ratio rd=Is/Ib of the surface (Is) to the bulk (Ib) dopant atomic fractions. At low temperature, Ts=400–570 °C the ratio maintains at the value rd≂1.5. For 570 °C≤Ts≤720 °C, rd increases to a plateau rd≂5.5, and then jumps to rd=42 in the 720–750 °C region. At higher temperature, Ts≥750 °C, rd decreases according to a relation which can be approximated by the classical equilibrium segregation theory. In that region, the boron Gibbs free energy of surface segregation is calculated from data to be ΔGS=−0.33±0.02 eV. Evolution of rd is closely correlated to the etch pit count and electron channeling results revealing amorphous, polycrystalline, and epitaxial growth, when going from low to high growth temperature.