Insituscanning tunneling microscopy (STM) has been used to examine the etching of ann‐Si(001) electrode in 0.1 M NH4F. Cathodic polarization facilitated chemical etching of Si(001) to give {111} microfacets as a result of the tendency of Si to form a monohydride terminated surface. Time‐dependentinsituSTM atomic images were obtained to demonstrate the preferential etching at the kinks and steps. From the results of the time‐dependent imaging, local etching rates were evaluated for the specific crystallographic directions. A Si(001):H‐(1×1) square structure was also obtained, demonstrating the presence of dihydride configuration in the beginning of the etching. ©1995 American Institute of Physics.