The detrapping current from polyethylene naphthalate (PEN) films γ-irradiated at doses ranged over 5×10,8,Gy was determined by using of thermally stimulated current technique with various electrode materials. The sign transition of main species of charge carriers in biaxial stretched PEN films has been observed. It was explained, that the sign transition results from shifting of sub-Fermi levels of electrons and holes, since the γ-irradiation induces decreasing of mean trap levels. The de-electreting phenomena of both amorphous and biaxial stretched PEN electrets have been investigated. The mechanism of moving of charge carriers during de-electreting has been discussed.