The influence of ammonia on silicon etching in HF/HNO3/H2O system was studied. Etching rates increase slowly with increasing volumes of ammonia when the amount of ammonia is small and then decrease with more additional ammonia. Consumption of the ammonium ion occurs continually accompanying the etching reaction. Etching weights of silicon and the temperature improvements in the solutions containing ammonia are larger than the solutions without ammonia if etching time is the same. Temperature, fluorine, and the decomposition of ammonium nitrate lead to the difference between the two solutions. Churning effect and diffusion layer theory are used to analyze the difference. (c) 2006 The Electrochemical Society.