Wire electric discharge machining (WEDM) of polycrystalline silicon (polysilicon) involves high-temperature melting that easily produces cracks on the wafer surface. This study explored the removal of surface defects by electrolytic machining (EM) to enhance surface quality. EM of polysilicon was conducted under different voltage supply modes, namely, DC voltage (DC-V), pulse voltage (Pulse-V), and auxiliary pulse voltage (Auxiliary-P-V) to examine their effects on material removal (MR) and surface roughness (SR). Results show that poor surface quality was achieved by EM with DC-V mode due to accumulation of bubbles between electrode gaps and inefficient MR. In contrast, EM with Pulse-V supply can reduce SR by proper control of pulse voltage cycle through adjustment in pulse-on and pulse-off time to ensure good replenishment of electrolyte. Finally, adding an optimal auxiliary voltage to the pulse cycle contributes to EM stability. Hence, EM with Auxiliary-P-V supply is an effective approach to electrolytic machining of WEDMed polysilicon. Not only is high MR achieved, but good surface quality is also maintained.