A new process combining inductive plasma torch and electromagnetic stirring of molten silicon in a cold crucible has been developed to refine upgraded metallurgical silicon. The addition of reactive gases to the plasma leads to volatilisation of impurities at the liquid silicon surface. The concentration of boron impurities decreased from 15ppmw in the raw material to less than 2ppmw after the plasma treatment, The most volatile form of boron was BOH, which was obtained by simultaneous treatment with oxygen and hydrogen. The limitation in boron volatilisation is due to the formation, at high oxygen flow rate, of a silica layer at the surface of the molten silicon, which results in a dramatic drop of the volatilisation rate, In contrast to boron, the concentration of phosphorus was reduced by only a factor of two, although the remainder seems to be electrically neutral. Thermodynamic studies suggest that phosphorus could be trapped as phosphate in combination with metallic impurities. Cells made of material produced using this technique exhibited a conversion efficiency of 12.4%. (C) 2002 Elsevier Science B.V. All rights reserved.