This letter studies the hydrogen plasma effects on the resistivity, effective free carrier concentration, and mobility of As+‐ and BF+2‐doped polycrystalline silicon (polysilicon) thin films of various thicknesses. It is found that the resistivity increases while the effective free carrier concentration decreases after the plasma treatment as the thickness of the polysilicon film decreases. The mobility typically tends to decrease for the thicker (≳60 nm) polysilicon film, but to increase for the thinner (<60 nm) polysilicon film. ©1995 American Institute of Physics.