Abstract: SiF.sub.4 gas containing oxygen-containing silicofluoride(s) typified by (SiF.sub.3).sub.2 O as impurity can be refined to extremely high purity by making the SiF.sub.4 gas contact with HF in the presence of a liquid medium having strong affinity for water such as sulfuric acid or phosphoric acid. By reaction with HF, the impurity such as (SiF.sub.3).sub.2 O is converted to SiF.sub.4, while the liquid medium absorbs water formed by the reaction to thereby prevent a reverse reaction between SiF.sub.4 and H.sub.2 O to form (SiF.sub.3).sub.2 O.

Abstract: A process of preparing silicon tetrafluoride by introducing hydrogen fluoride gas into a dispersion of powdery silicon oxide material, which needs not to be pure SiO.sub.2, in sulfuric acid not lower than 65% in the concentration of H.sub.2 SO.sub.4. The reaction takes place even at room temperature. By using amorphous silicon oxide material, the rate of reaction can be enhanced with better yield. Preferably, the concentration of H.sub.2 SO.sub.4 in the liquid phase of the reaction system is maintained above 80% to obtain SiF.sub.4 containing little (SiF.sub.3).sub.2 O.