The influence of moisture on plasma etched polyimide (PI) films is reported. Reactive ion etching plasmas with different CF4/O2ratios (0%–30% CF4) are used to etch metal–polyimide–metal parallel plate capacitors. Plasma etching leads to a geometrical modification of the capacitor structures studied. This results in a reduction of the device capacitance which is modeled using a three‐dimensional Poisson solver (seses). A Debye type dielectric relaxation is observed in O2/CF4plasma treated capacitors when measured at 85% relative humidity. The location of the loss peak is found to be dependent on CF4/O2ratios. Wet capacitors do not exhibit this loss peak prior to etching. The observed relaxation in plasma treated PI capacitors can be removed by reheating to the cure temperature. A Debye model is used to extract a RC equivalent circuit for the etched capacitor structures. In parallel, x‐ray photoelectron spectroscopy (electron spectroscopy for chemical analysis) is used to monitor the chemical changes in PI due to plasma treatment, and the observed chemical and dielectric changes are correlated.