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In this letter, we presented a self-assembled microlens array (MLA) fabricated by use of the hydrophilic effect under ultraviolet (UV)/ozone treatment. This method provides a fast, simple, and low cost process. It does not require lithography or etch-transfer processes. The MLA was made of negative photoresist SU-8 (n=1.63 at 530 nm) on a glass substrate. Microlenses from 50- to 200-μm diameters were successfully fabricated by using this method. A 10-μm-thick shadow mask was used to define the UV/ozone treatment area to create more hydrophilic surfaces on an SU-8 photoresist base layer on a glass substrate. After hydrophilic zones were created, the glass substrate was immersed into a diluted SU-8 photoresist solution and was removed out of the solution. Finally, the MLA was formed after the UV curing process. The relationships between the focal length of the MLAs and UV/ozone treatment time were systematically investigated.