Indium–tin–oxide (ITO) coated on a glass plate as the transparent electrode in polymeric light‐emitting diodes (LEDs) generates some volcano‐like patterns during use especially at a higher applied electric field strength. Such an ITO damage phenomenon is independent of Joule heat, conjugation structure of the polymer, and light‐emission process, but only dependent on the applied electric field strength. The ITO damage, which results from a self‐decomposition reaction, can cause a reduction of lifetime of the device. ©1996 American Institute of Physics.