A comparison of and trichloroethylene (TCE) as chlorine bearing gaseous additives to the oxidizing ambient for growing thermal oxide on silicon at 1150°C was made. According to a thermodynamic analysis of the gas phase species at comparable partial pressures of chlorine in the reactor, the major difference in the gas phase composition is about an order of magnitude lower partial pressure of and in the TCE system. The parabolic rate constants at 1150°C at approximately the same partial pressures of in both systems over a range of input feed rates of 0–120 cm3/min per liter of dry (and comparable rates of mixture) were similar, being only marginally lower for the TCE system, although the equilibrium and contents of the TCE reactor were an order of magnitude lower. The addition of and TCE were both found to result in significant increases on inversion times of carriers as determined by capacitance vs. time measurements of pulsed MOS capacitators.