The etching reaction of molecular chlorine with phosphorus‐doped polycrystalline silicon was measured as a function of dopant concentration between 300 and 500 °C. The effective activation energy of the gasification reaction is 13.4±1 kcal/molec and does not change with doping level within experimental uncertainty. However, the isothermal reaction rate at constant reactant flux increases sharply with doping level, and the preexponential factor rises from 4×10−12to 1×10−10(A˚ cm3/molec min K1/2) as the phosphorus content is increased from 3.3×1018to 1.6×1020atoms/cm3. This rise in the preexponential factor is consistent with the charge‐transfer model, in which doping makes Si‐Cl bonding more ionic and increases the number of effective adsorption sites.