This is actually not such a simple question as it seems! The reason being that even those thermocouples designed for extremely high temperatures have a maximum range that can be significantly affected by factors such as the;
However, generally speaking, refractory metal tungsten-rhenium thermocouples Type C and Type D are considered the highest temperature thermocouples, capable of being used for temperature measurement up to 2300ºC, provided it is not an oxidizing environment.
You can read more about thermocouples Type C (W5%Re-W26%Re) and Type D (W3%Re-W25%-Re), their differences and applications on our product page.
In an oxidizing environment the noble metal platinum-rhodium thermocouples Type R (Pt13%Rh-Pt), Type S (Pt10%Rh-Pt) and Type B (Pt30%Rh-Pt6%Rh) are considered the highest temperature thermocouples with a maximum range varying from 1400ºC up to 1700ºC.