Oxygen and nitrogen impurities increase the dark conductivity of hydrogenated amorphous silicon (a‐Si:H), due to their donorlike behavior. An appropriate amount of boron doping recovers these values to the original ones unless the effect of band gap widening appears. The midgap absorption spectra of the compensateda‐Si:H are identical to those of intrinsica‐Si:H both at initial and light‐soaked states. The major effect of the oxygen and nitrogen is the creation of donors, which show a similar behavior to those by phosphorus—only a small fraction of the oxygen and nitrogen produces donors, the rest is included in thea‐Si:H network without causing any other significant effect until alloying effects appear. ©1996 American Institute of Physics.