This paper proposes a new way to detect the gas-leakage through PDMS. We use PDMS instead of Pyrex #7740 glass to seal the backside V-grooves of silicon pressure sensors. We put the packaged sensor into a pressurized chamber with CO2 at 300 psi. By observing the output voltage of the pressure sensor, the time history for CO2 permeating into the sensor cavity was easily found. In experiments, we use several PDMS membranes with different thickness, from 45 to 2000 μm, to package the pressure sensors and investigate the gas-leakage of PDMS. The gas leaking through PDMS is shown to be governed by diffusion mechanism, and the diffusion coefficients derived from CO2 leaking history is 2.2×10-9 m2/sec, matched with the previous work.