The evolution of the electrical activation with the annealing time in B+implanted (5.0×1014cm−2, 50 keV) Si was studied as a function of the annealing temperature. Electrical activation yields of 15%–30% were observed after annealing for 2 s at temperatures above 550 °C. Prolonging the annealing time from 2 to 900 s we observed that the electrical activation evolves differently according to the temperature: (i) at 550 °C<T<700 °C it decreases toward an equilibrium level, (ii) at 700 °C<T<800 °C it decreases during the first minutes and subsequently increases again, and (iii) at temperatures <550 °C orT≳800 °C it increases continuously. In order to explain the carrier removal observed during annealing at 550–800 °C we proposed that metastable acceptor centers are formed during the B+implantation and/or the initial period of the annealing time. Interaction of Si self‐interstitial atoms with these centers leads to their neutralization and/or dissociation with consequent decreasing of the carrier concentration. ©1995 American Institute of Physics.