Abstract For enhancing the surface finish of micro-holes, micro-EDM and micro-ECM have been combined in a unique hybrid machining process by using low-resistivity deionized water as bi-characteristic fluid. The affected material layer generated by electric sparks is further dissolved from machined surface owing to the effect of electrochemical reaction. To maintain the dimensional accuracy of micro-holes, short voltage pulses are applied to localize the material dissolution zone and thus the thickness of further removed material layer is of prime importance in deciding the final dimension of micro-holes. This study presents the modeling of radial gap distance in simultaneous micro-EDM and micro-ECM drilling by predicting the thickness of material layer further dissolved by electrochemical reaction. The analytical approach incorporating the double-layer theory, the Butler–Volmer equation and the Faraday's law of electrolysis is used to simulate the radial gap distance for different pulse parameters. The simulation data is then verified with the experimental results. It is observed that the applied pulse parameters directly affect the final dimension of obtained micro-holes. The effectiveness of short voltage pulses in localizing the material dissolution zone is found to be in accordance with the double-layer charging characteristic. When the pulse duration is too short, the material dissolution is negligible and SEDCM has no effect on improving the inner surface of micro-hole.