We present analytical and computational models used to investigate the dependence of etch resolution on pulse duration, tool radius, and etched feature aspect ratio in electrochemical machining with ultrashort voltage pulses. Our results predict that, for the high aspect ratio system in which the effect of trench top and bottom edges can be ignored, the increase of etch resolution with pulse length is a strong function of tool radius, while there is a significant dependence on etch depth for the low aspect ratio system in which the edge effects become important. A detailed analysis of the etch trends is presented. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.2136250] All rights reserved.