Anisotropic etch rates of silicon in KOH solutions were studied as a function of an externally applied potential. A combination of three micromachined samples consisting of predry-etched wagon-wheel patterns and masked trench offset patterns was used to measure the etch rates at a large number of crystal orientations simultaneously. The measured data was described in terms of microscopic properties, including step velocities, terrace roughening, and step anisotropy, using the kinematic wave etch model. All parameters show distinct changes due to the applied potential and resulting additional electrochemical reaction path. A decrease in step velocity shows the electrochemical oxidation and subsequent passivation of the Si surface. Trends in terrace roughening show a minimum in roughness and a corresponding change in anisotropic etch-rate ratio at the non-open-circuit potential of -1250 mV vs saturated calomel electrode. The observed decrease in step anisotropy and subsequent step-anisotropy reversal at more positive potentials indicates an anisotropy in not only chemical etching but also electrochemical oxidation of (111) surface steps. (c) 2007 The Electrochemical Society.