We report on concomitant measurements of the metastable light‐induced excess conductivity &sgr;eand of the defect density Ndin two series of n‐type a‐Si:H films doped with 30 or 300 ppm B2H6, respectively, and various volume parts of PH3. The data for &sgr;eare analyzed in terms of the light‐induced shift of the Fermi level, &Dgr;Ef. This quantity is determined by the density Neof light‐induced centers providing the negative excess charge (E‐centers) and by the density of states at the Fermi level, g(Ef). The changes of Neand g(Ef) give rise to the complicated dependence of &Dgr;Eton the exposure time teand on the Fermi‐level position, Ec−Ef, in the films. We also present data on the formation and annealing kinetics of the E‐centers. Their possible nature is discussed in the light of recent ideas on the mechanism of metastable phenomena in a‐Si:H films.