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In this paper, polymer-based microcryogenic cooler (MCC) cold stages, each with a footprint of 17 mm × 5 mm, have been successfully developed and tested. The MCC cold stage consists of a polyimide heat exchanger (HX) which is monolithically manufactured on a silicon substrate by using a polyimide/copper microelectromechanical systems process and a silicon/glass Joule-Thomson (J-T) valve which is formed with anodic bonding. Specifically, PI-2574 (HD MicroSystems) was used to make the HX in this work. The two parts are assembled together, forming a cooler which uses the J-T cycle. A cooling test with an optimized five-component mixture as the refrigerant was conducted to examine the performance of the cooler. The cooling temperature was able to reach 233 K under an operating pressure ratio of 0.7:0.15 MPa. It is one of the world's smallest J-T cold stages and the first one fabricated and assembled based on wafer-level processes.