Herein, we report that the organic superbase t-Bu-P4 catalyzes the demethylation reactions of methoxyarenes in the presence of alkanethiol and hexamethyldisilazane. The system can efficiently convert a variety of substrates, including electron-deficient, -neutral, and -rich substrates and heteroaromatic substrates, and displays excellent functional group tolerance. Computational studies show that the high reactivity achieved by t-Bu-P4 is due to the formation of the nucleophilic naked thiolate species.