The silicon etching process in the HF/HNO3/H2O system with abundant HNO3 has been studied. Since the etching rate and the reaction temperature are changing along with the time passed, the process could be divided into five stages. During the whole process, the concentration of F- in the solution decreases gradually. The results of variation of the etching rate showed that there are factors-the heat generated, the concentration of the F-, and the heat exchange between the system and the environment.