The diffusion of boron ions implanted in Si(100) during high temperature treatment has been studied by means of Secondary Ion Mass Spectrometry. The boron ions were implanted at energies of 5 and 10 keV along random direction and along . The implantation dose amounted to 1×1013/cm2. During annealing an enhanced diffusion of boron is observed in the tail region of the implantation profiles. In all cases the enhanced diffusion is completed after Rapid Thermal Annealing at 900°Cfor 10”. The enhanced diffusion is largest for the channeled ion implantations. Channeling analysis shows that the transient diffusion is not correlated with the annihilation of defects near the projected range. Therefore, the observed diffusion tail is attributed to rapidly diffusing interstitial boron. Post-amorphization of boron implanted silicon with Si+ ions is used to prevent transient diffusion. Thus a very sharp pn-junction is obtained at a depth of 03 jim and the effective number of charge carriers equals the implanted dose after annealing at 550°Cfor 5hrs and 1000°Cfor 10”.