The paper presents a novel and economic manufacturing process for microlens arrays (MLAs). This process uses micromilling machining, PDMS casting, and hybrid bonding between a glass substrate and PDMS membrane to create a microfluidic chip which is used for manufacturing MLAs on a PDMS substrates. MLAs of various diameters were fabricated for experiments, including 1000 μm, 500 μm, and 200 μm. The sag height of the MLAs is easily adjusted by controlling the pressure inside the microchannel to deform the PDMS membrane. Multiple experiments were conducted to characterize the performance of MLAs, the results of which demonstrate: (1) this fabrication process is able to manufacture MLAs with various dimensions and the diameter of an MLAs is determined by the size of micromilling bit and cutting path; (2) the sag height and curvature of MLAs can be controlled by the PDMS membrane thickness and the hydraulic pressure inside the microchannel; (3) an optical system was built to investigate the uniformity of MLAs and the experiment results showed uniform focal length of MLAs; (4) the resulting MLAs magnify tiny objects and significantly enhance the fluorescence signal emitted from the microchannel.