We have characterized metastable states in n‐type doped a‐Si:H due either to fast (quench) cooling or by light‐soaking followed by a series of partial dark anneals. These studies have been carried out for samples with a large range of PH3doping levels using drive‐level capacitance profiling to deduce the number of occupied bandtail states (NBT) and transient photocapacitance spectroscopy to measure the density of deep defects (ND). By comparing the changes in these quantities we are able to distinguish among many of the metastable defect reactions that have been proposed. In particular we have found conclusive evidence that quench cooling, although increasing NBTtypically by a factor of 2, does not modify NDin any of our samples. Marked changes in NBTwith negligible changes in NDare sometimes also obtained for some of the partial anneal steps following light‐soaking. These results are discussed in terms of possible defect reactions which can activate a phosphorous dopant atom without simultaneous formation of silicon dangling bonds.