[en] Transition metal dichalcogenide (TMDC) monolayers have attracted great attention due to their unique electronic properties, which promise their applications especially in optoelectronics and valleytronics. A simple and reliable way to fabricate the monolayers is highly desirable for wide applications. Herein, we report a photo-induced exfoliation method for the controllable fabrication of monolayer TMDCs proceeded with the oxidation reaction of TMDCs by the photo-generated holes. The commonly used microscope halogen lamp is sufficient to initiate the exfoliation in pure water. A bulk MoS₂ flake with a surface area of 10 000 µm² and a thickness of 100 nm can be directly exfoliated down to monolayer within four seconds under a 94 nW µm⁻² 660 nm laser illumination and by applying 0.1 V potential electrochemically, achieving an astonishing exfoliation speed and efficiency. This method is demonstrated to be applicable also to other semiconducting TMDCs, such as MoSe₂, WSe₂, and WS₂. (paper)