The long-time transient photocurrent decay in annealed and light-exposed P-doped a-Si: H is examined experimentally and by numerical modelling. The decay is a dispersive power law with sublinear index, extending to times longer than 1s, and the decay rate increases with temperature. Light exposure dramatically decreases the decay amplitude but does not affect the rate of decay. The phenomenon is discussed in terms of a comprehensive multiple-trapping model in which transport of thermalized electrons is essentially non-dispersive, and recombination of free carriers via defects is dispersive, owing to continued thermalization of excess holes. The slower recombination step is free-hole capture by D−states, while the decay of the total excess ensemble is controlled by hole release from valence-band tail traps. The index of the excess photoelectron decay provides information on thevalence-bandtail states, which are exponentially distributed, with a characteristic energy estimated as 0·06 eV.