The stable gas products of germane dissociation and subsequent radical reactions have been measured in pure germane glow discharges characteristics of the initial germane fragmentation are inferred from these data. The spatial distribution of discharge optical emission, and of film deposition on glass fibers, have also been measured. Finally, the surface reaction probability &bgr; of depositing neutral radicals has been measured to be 0.61±0.09 on the grounded electrode. Major differences between germane and silane discharges occur in all these observables. Possible explanations of these differences are given, but much less chemical data exists for germane, thereby precluding definitive judgments. A probable cause of the normally much poorer semiconductor quality ofa‐Ge:H films, compared toa‐Si:H, is suggested. This is based on the thermodynamics of the H2release reaction at the growing surface.