In this study, ozone-activated peroxymonosulfate (O₃/PMS) was used to remove tetramethylammonium hydroxide (TMAH) from artificial semiconductor wastewater. The rate constant for the O₃/PMS process was approximately 14.4 times higher than that for the process employing only O₃. This was attributed to the explosive production of hydroxyl radicals (•OH) in the process, the contribution of which was confirmed using a scavenger test. The degradation efficiencies were the highest at pH 7.0 (1.80 × 10⁻² min⁻¹) and 40 °C (2.18 × 10⁻² min⁻¹). Alkalinity and humic acid, which are potent scavengers of •OH, significantly reduced the degradation of TMAH. Remarkably, removal efficiencies of 64.4 % for TMAH and 43.7 % for the total organic carbon (TOC) were achieved at a relatively high initial concentration of 100 μM. However, approximately 27 % of the nitrogen was converted to the final byproducts, NH4⁺ and NO₃⁻, indicating that a considerable number of nitrogen fragments remained as intermediates. Degradation pathways and intermediates were proposed based on the spectrometry data. Given that the toxicity of the demethylated intermediates was roughly 20–30 times lower than that of TMAH, the acute toxicity to A. fischeri was reduced by approximately half (46.4 ± 2.57 %). The results of this study demonstrated the substantial potential of the O3/PMS process for treating wastewater containing TMAH.