The silicon etching rate by chlorine trifluoride gas is systematically studied using a reactor having a very small cross section above the silicon substrate and achieving a very high efficiency of etchant gas consumption and very large etching rate, larger than 20 mum min(-1). The silicon etching rate is shown to be proportional to the flow rate of the chlorine trifluoride gas. However, this rate is, for the first time, found to be independent of the initial silicon substrate temperature. This study shows that the silicon substrate is automatically heated to the temperature determined by the balance of the reaction heat and the heat transport in the reactor. Since this temperature increment processes an extremely large-surface chemical reaction rate, the etching rate is governed by the transport rate of the chlorine trifluoride gas. This study concludes that a high efficiency silicon etching by chlorine trifluoride gas is possible without any supplemental heating. (C) 2003 The Electrochemical Society.