Organic electroluminescent device (OLED) was fabricated using a vacuum evaporation method and thermal properties were investigated. The OLED has an indium tin oxide (ITO)/N,N'-Biphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD)/tris(8-hydroxyquinoline) aluminum (Alq)/lithium fluoride (LiF)/aluminum (AI) structure. An electron-dominant device of Al/Alq/LiF/Al structure, or it hole-dominant device of ITO/TPD/Al structure was also fabricated in order to study the carrier behavior in the OLEDs. The current density versus voltage (J-V) properties with various thickness of organic layers were investigated in both electron- and hole-dominant devices, and the thermal dependence of J-V properties was observed in the devices. At room temperature, conductions in a wide current region were considered to be due to space-charge-limited current for all of the devices. Especially for the Al/Alq/LiF/Al device and the OLED, J proportional to V(m+1) relationships were observed across a wide current region. At low temperature, tunnel currents were estimated for the ITO/TPD/Al device. For the Al/Alq/LiF/Al device and the OLED, J proportional to V(m+1) relationships were observed across a wide current region at low temperature. (C) 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(3): 24-31, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10048