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A new characterization method for charge conditions in electret polymer films is proposed. This method uses the change of the threshold voltage in an EEPROM (electrically erasable and programmable read-only memory) device to evaluate the effective charge density in electret. The EEPROM device has an extended floating gate that is capacitively coupled to a sensing gate in direct contact with the electret polymer film. It also has a control gate similar to that in the conventional EEPROM device driven by test signals. By the total capacitive loads and effective charges seen on the floating gate, the surface potential of the transistor channel in the subthreshold region is a linear function of effective electret charge density. Representative measurements with several electret charging conditions, such as photo poling and mechano poling are provided. With the bandwidth of the EEPROM device typically much higher than 1 kHz, real-time charging characteristics with sub-millisecond resolution can be obtained.