The temperature stability of OLEDs was investigated by observing the I-V and EL-V characteristics of various devices stored at elevated temperature (up to 140 degrees Celsius). Results reported in this paper concern the standard KODAK structure for a green OLED (i.e. anode/CuPc/NPB/AlQ3/cathode), the standard IDEMITSU structure for a blue OLED (i.e. anode/CuPc/NPB/DPVBi/AlQ3/cathode) and variants of those using high Tg materials consisting of a spiro- bifluorene core. Use of Spiro-TAD as a hole transport material (HTM) and of Spiro-DPVBi as an emitting material (EM) resulted in considerable improvements. While the initial performance of the virgin devices is considerably unchanged, the temperature stability increases dramatically: for the green OLED no significant deterioration up to 140 degrees Celsius is found, compared to the standard device including NPB already starting to degrade slightly above 100 degrees Celsius; the blue OLED is stable up to approximately 120 degrees Celsius (particularly the color coordinates of the emitted light) whereas the standard device using DPVBi already deteriorates at around 80 degrees Celsius.