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The presence of ZnS precipitates is common in Cu2ZnSnS4 (CZTS) films due to the preferred Cu-poor and Zn-rich composition for high-efficiency CZTS devices. It is important to identify their distribution in the film as it can serve as a fingerprint for the CZTS forming process. However, limited methods are viable to quantify their distribution as they are small in size and few in number. Herein, a fast and cost-effective chemical treatment is presented that can reveal the nanoscale ZnS domains within CZTS films to be captured under a common scanning electron microscope (SEM). This method exploits a hole-injection process driven by gold catalysis and the band alignment between CZTS and ZnS. ZnS precipitates as small as 10 nm in diameter can be revealed clearly. Using this approach, a characteristic lognormal size distribution of the ZnS precipitates close to the CZTS film surface with a median diameter of 80 nm and a density of around 2 in a 1 μm² surface area is demonstrated. Energy-dispersive X-ray spectroscopy (EDS) mapping and scanning transmission electron microscopy (STEM) imaging further confirm the existence of ZnS precipitates in the film. This method provides a fast means for capturing fingerprints of ZnS precipitations in CZTS process. [ABSTRACT FROM AUTHOR]