As‐deposited undoped microcrystalline silicon (&mgr;c‐Si:H) has in general a pronouncedn‐type behavior. Such a material is therefore often not appropriate for use in devices, such asp‐i‐ndiodes, as an active, absorbingilayer or as channel material for thin‐film transistors. In recent work, onp‐i‐nsolar cells, this disturbingn‐type character had been successfully compensated by the ‘‘microdoping’’ technique. In the present letter, it is shown that thisn‐type behavior is mainly linked to oxygen impurities; therefore, one can replace the technologically delicate microdoping technique by a purification method, that is much easier to handle. This results in a reduction of oxygen impurities by two orders of magnitude; it has, furthermore a pronounced impact on the electrical properties of &mgr;c‐Si:H films and on device performance, as well. Additionally, these results prove that the unwanted donor‐like states within &mgr;c‐Si:H are mainly due to extrinsic impurities and not to structural native defects. ©1996 American Institute of Physics.