The mechanism causing the behavior of the silicon etch rate using chlorine trifluoride gas, which appears to be independent of the substrate temperature in a horizontal cold-wall reactor, is clarified by means of numerical calculations taking into account the surface chemical reaction rate on the silicon substrate surface and the transport phenomena in the entire reactor. The activation energy of the overall rate constant of its surface chemical reaction is evaluated, for the first time, to be 6000 J mol(-1), which can reproduce the etch rate and its behavior obtained by the measurement. With increasing substrate temperature in the reactor, the effect of a moderate increase in both the diffusivity of chlorine trifluoride gas and the overall rate constant is considered to be compensated by the decrease in the chlorine trifluoride gas concentration due to the gas volume expansion in the gas phase above the substrate. Therefore, the etch rate can be independent of the substrate temperature. (C) 2004 The Electrochemical Society.