The etching reaction of silicon in HF-KMnO₄-H₂O mixed solution has been studied under various experimental conditions. The etch rates were measured as a function of agitation speed, HF and KMnO₄, concentrations, and etching temperature and time. A comprehensive mechanism for the silicon etching and insoluble solid-phase film(K₂SiF_6) formation has been proposed. The holes formed at silicon surface accelerated not only the etch rate of silicon but also the formation rate of K₂SiF_6. With the increase of hole concentration at lower HF concentrations the etch rates decreased because of the deposition of K₂SiF_6 on etched silicon surface. Under the condition of sufficiently high HF concentration, the rate increased with the increase of hole formation and the formation of holes at silicon surface was the rate limiting step of the silicon etching reaction in HF-KMnO₄-H₂O solution. High HF concentration enough for dissolving K₂SiF_6 was apparently essential to obtain high etch rate in the silicon etching reaction.