This communication reports on the effect of thermal annealing on the physicochemical and electrical properties of boron doped amorphous silicon thin films deposited by reactive magnetron sputtering in a mixture of argon and hydrogen atmosphere. The IR absorption spectra of as prepared samples exhibit the peaks characteristic of Si-H, Si-B and B-H bonding vibrations. After annealing, our analyses revealed some modifications in the peak characteristic of B-H bonding, while no significant increase in Si-B peak intensity was observed. In other respects, electrical measurements showed an increase in the conductivity from 10-8 to 10-5 -1 cm-1 and a decrease in its activation energy from 0.57 eV to 0.33 eV after a successive annealing at temperatures varied between 150°C and 450°C. These results showed that boron doping becomes increasingly efficient after annealing, which could be assigned to the reduction in the content of hydrogen playing an important role in the passivation of boron atoms.