In this work we present the elevated temperature operation of carbon nanotube thin film transistors up to 100 °C in air ambient. It is demonstrated that for semiconducting nanotubes the OFF current leakage does not increase and the high ON/OFF ratio of transistors consisting of semiconducting nanotubes is preserved up to 100 °C. In addition, we investigate the factors affecting the operation of carbon nanotube transistors at high temperature for a range of source-to-drain spacing and metallic tube contents. The influence of change in tube-tube and tube-metal contact resistance on the device characteristics at high temperature is demonstrated. © 2011 American Scientific Publishers.