The etching of silicon has been studied by the scanning electrochemical microscope (SECM) technique. Etching has been accomplished in acidic fluoride solutions by electrogenerating a strong oxidant, i.e. bromine in this case, at an ultramicroelectrode which was held closely above a silicon 〈111〉 wafer. The parameters that affect the process and control the efficiency of the silicon etching were examined. A detailed mechanism of the process, which was derived from the unique advantages of the SECM and is in agreement with previous reports, is proposed.