Abstract— Thermal models and tests of active‐matrix OLEDs (AMOLEDs) show that thermal effects can significantly reduce the lifetime of an OLED device. A comparison of the experimental heat distribution in an AMOLED with thermal models demonstrates that the thermal resistivity of the organic layers in an OLED is surprisingly high. Experiments with AMOLEDs show that the lifetime of OLED devices can be significantly improved through the use of heat‐spreading layers in the OLED devices.