As‐deposited undoped microcrystalline silicon (μc‐Si:H) has in general a pronounced n‐type behavior. Such a material is therefore often not appropriate for use in devices, such as p‐i‐n diodes, as an active, absorbing i layer or as channel material for thin‐film transistors. In recent work, on p‐i‐n solar cells, this disturbing n‐type character had been successfully compensated by the ‘‘microdoping’’ technique. In the present letter, it is shown that this n‐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 μc‐Si:H films and on device performance, as well. Additionally, these results prove that the unwanted donor‐like states within μc‐Si:H are mainly due to extrinsic impurities and not to structural native defects. © 1996 American Institute of Physics.