This study demonstrated a new thermo-pneumatic micropump implemented by stacking three layers of PDMS on a glass slide. The pumping with valve-less diffuser/nozzle channel is driven due to the flow rectification effect. The large actuation stroke of the deforming diaphragm appears as the phase change from the working liquid into vapor inside the evaporation chamber by the Joule heating of the embedded heaters. With the wall temperature of PDMS below 50 C verified by an infrared imager, the pumping flow rates are 3.5–12.5 nL/min subject to a square wave of 4 V peak-to-peak heating voltage with frequency varied from 0.3 to 3.0 Hz. After coating the micropump inner wall with a 3 lm Parylene against the gas leakage through PDMS, the micropump paid the price of decreasing the flow rate down to 2.5–6.5 nL/min.