Tetrafluorosilane is produced by a process comprising a step (1) of heating a hexafluorosilicate, a step (2-1) of reacting a tetrafluorosilane gas containing hexafluorodisiloxane produced in the step (1) with a fluorine gas, a step (2-2) of reacting a tetrafluorosilane gas containing hexafluorodisiloxane produced in the step (1) with a highvalent metal fluoxide, or a step (2-1) of reacting a tetrafluorosilane gas containing hexafluorodisiloxane produced in the step (1) with a fluorine gas and a step (2-3) of reacting a tetrafluorosilane gas produced in the step (2-1) with a highvalent metal fluoxide. Further, impurities in high-purity tetrafluorosilane are analyzed.