They have tested their devices at 300 Celsius degrees, but significantly higher temperatures should be possible, e.g. 500 or 600 Celsius degrees. It is likely

They have tested their devices at 300 Celsius degrees, but significantly higher temperatures should be possible, e.g. 500 or 600 Celsius degrees. It is likely that the upper working temperature would not be limited by the semiconductor channel, but by the accelerated degradation of the metallic conductors, which would limit the lifetime of the devices. Conductors with better chemical and electromigration resistance would have higher electric resistivity, lowering the speed of the devices.