What is the temperature range of the thermosphere?

Above 120 miles (200 km) above sea level, temperatures in the thermosphere can vary between 600° and 2000°C (1100 and 3600°F).

The actual temperature range is highly dependent on solar activity.

A longer answer
The thermosphere is a layer of Earth's atmosphere above the mesosphere. The thermosphere extends from 50 to 55 miles (80-90 km) above sea level, with the upper limit undefined.

The temperature in the thermosphere initially rises rapidly with heights up to about 120 miles (200 km) and thereafter increases more slowly. Above 120 miles (200 km) - depending on solar activity - the temperature varies between 600° and 2000°C (1100 and 3600°F).