The incomplete activation observed when high doses of boron (2×1015−2×1016ions/cm2) are implanted in silicon is characterized by a maximum concentration of electrically active boron that is independent of both the dose and anneal time and well below the solid solubility value. An Arrhenius plot for this concentration‐temperature dependence yields an activation energy of 0.31 eV. It is suggested that the incomplete activation is due to interactions between the implanted ions. Whether the defect structure is a simple B&sngbnd;B pair or a cluster involving residual damage is not clear at this time.