Silicon tetraiodide is formed from commercial silicon and iodine in a fluid‐bed reactor. Impurities are rejected by solvent recrystallization followed by fractional distillation. High‐purity silicon is formed by thermal decomposition of the iodide on a silicon surface. Silicon made this way has a resistivity over a 1000 ohm‐cm. Reproducible results are obtained which suggest the product quality is controlled by back‐contamination from the decomposition and crystal growing steps. Data from the decomposition of silicon tetraiodide at 1000°C and low pressure are correlated by the relation: where vapor feed/hr/ft2 heated surface and . It is postulated that this reaction reaches equilibrium.