Dopant activation occurs via both thermal annealing and light‐soaking in boron‐doped hydrogenated amorphous silicon–carbon prepared at a relatively low temperature. Both kinds of dopant activation probably originate from the same boron sites, because they both cause almost the same increase in dark conductivity, and no light‐induced activation occurs after the thermally induced activation has been attained. The light‐induced states show relaxation even at room temperature and are bistable sites, but the thermally induced states show no significant relaxation and have a more stable configuration. Perhaps, the light‐induced states are caused by microscopic change and the thermally induced states are created with larger scale restructuring. ©1996 American Institute of Physics.