Hydrogenated amorphous silicon films 0.45 and 1.12μm thick, grown by RF glow discharge plasma PECVD on Coming-7059 glass, were irradiated by a o 6 0 Co source (activity 2.8 10 1 5 Bq) in the dose range 10-450 kGy at different dose rates. The dark current of the samples, under 100 V applied voltage, was measured before, during and after gamma irradiation. When the irradiation starts, the dark current increases up to a level linearly dependent on the dose rate. When the irradiation is switched off, the dark current returns close to the initial value in a few days. Such behaviour suggests a possible application of hydrogenated amorphous silicon films in dosimetry and as gamma ray sensors. Moreover, the film optical constants were computed from the transmittance spectra measured in the range 500-2500 nm, before and after irradiation. After irradiation, the film optical absorption is slightly increased and the energy gap is substantially unchanged.