A new microwave plasma process is developed to refine and purify metallurgical grade silicon (MG-Si) effectively. Inductively coupled plasma-atomic emission spectrometry analysis (ICP-AES) indicates that the concentrations of impurities in silicon decrease significantly in the process, particularly for phosphorus, whose average removal rate is close to 100% after microwave plasma treatment of only 5 min. The underlying mechanisms of the ultra-high removal rate of impurity atoms are discussed in detail in this paper. The photoresponse switching behavior of n(+)-Si wafers that are made of as-purified silicon provides further evidence for the unique advantage arising from the use of microwave plasma in the purification of MG-Si. (C) 2012 Elsevier B.V. All rights reserved.