The electrical properties of grain boundaries have been investigated by means of capacitance measurements such as deep‐level transient spectroscopy and thermally stimulated capacitance. This paper describes the evolution of the electrical properties ofn‐type &Sgr;=25 silicon bicrystals as a function of heat treatments. It results from this work, that after annealing and quenching, the &Sgr;=25 bicrystal presents an electrical activity and that metallic impurities are responsible for the grain boundary electrostatic potential barrier. The investigations by transmission electron microscopy have shown that the grain boundary activity is in relationship with the presence of colonies of precipitates at the interface, these precipitates being silicides. The results of microanalysis experiments made elsewhere on other similar bicrystals indicate the presence of copper and nickel in the precipitates forming the colonies. The importance of the heating and cooling rates of the samples about the energy distribution of the interface states display the kinetic aspect of the mechanisms involved (segregation‐precipitation).