Cyclic dehydrogenation-rehydrogenation experiments have been performed on p-type poly-Si/SiO x stack to study the roles of hydrogen (H) atoms for crystalline silicon (c-Si) surface passivation. The effective lifetime of minority carriers is enhanced to 1.4 ms by the hydrogenation of hydrogen plasma treatment (HPT) at 300 °C. The dehydrogenation by thermal annealing at 450 °C decreases the lifetime to ∼0.6 ms, which is recovered by a consecutive HPT, underlining the c-Si surface passivation by H atoms diffused into the SiO x /c-Si interface. The lifetime recovery follows a stretched exponential function, indicating the dispersive nature of the p-type poly-Si/SiO x stack. © 2019 The Japan Society of Applied Physics °C under 0.5 Torr with a power density of 60 mW cm −2 . Between each process and characterization step, the samples are kept under vacuum to avoid unintentional oxide growth