It is revealed for the first time that single atomic steps with a height of 0.14 nm on a Si(100) surface in air can be clearly distinguished by using a laser confocal microscope combined with an advanced differential interference contrast microscope (LCM-DIM). Images of LCM-DIM were acquired in wider areas than 100 mu m(2) within a shorter period of time than a few second. Furthermore, even in electrolyte solutions, the single atomic step can be seen by the new technique, which will be able to apply to the evaluation of dynamic processes of chemical and electrochemical etching of Si surfaces. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3597657] All rights reserved.