We observed the current‐voltage characteristics of a‐Si:H diodes having nin‐ and pip‐structures after annealing, bias stressing and photo stressing. Both diode types show photo degradation, the pip diodes also bias degradation. The degradation is reversible in all cases by annealing. Furthermore, photo and bias degradations proceed independently of each other. We conclude that recombination and hole trapping induce different metastable defects.