The paper studies the metastable state of bias annealed P-doped a-Si with an improved sweep-out technique. Direct measurement of n BT up to 500 K and effective bias annealing were achieved by incorporating a thin SiN x layer in the sample design. Reverse bias annealing on specimens of PH 3 doping levels between 0.2 and 20 vppm produces a metastable state with greatly increased active donor density. In all the cases saturation of n BT with the biasing potential has been observed and it is suggested that under such conditions all P-sites have been converted into the P + 4 configuration. From the saturation level the density of the incorporated P can be obtained. The time dependence of the dopant activation process during bias annealing follows a pure exponential law, contrasted to the stretched exponential relaxation process. The time constants of these processes, τ ACT and τ REL, are the same and their temperature dependence has an activation of 1.0 eV. It is pointed out that the pure exponential law provides a strong support for the single step process in removing the H from a H-passivated donor site.