Together, HKUST and IMECAS are investigating the potential of gallium nitride (GaN)-based electronic devices for extreme temperatures, ranging from cryogenic (~4 K) to ultra-high (>600 K). Three categories of GaN electronic devices are being studied for different ExTemp scenarios: power switches, radio-frequency (RF) power amplifiers, and logic circuits. The project aims to identify and classify GaN-based semiconductor technologies for different extreme temperatures, highlighting their advantages and understanding the physics linking GaN's properties to application demands through thorough characterisation, modelling, and analysis. In addition, using these insights, the project will enhance promising GaN devices for improved ExTemp resilience and encourage their use in real-world applications through innovative design and fabrication processes. This involves developing innovative device designs and improving manufacturing techniques to withstand extreme temperatures, ultimately promoting the adoption of these advanced GaN devices in practical applications. Through experimental validation, it seeks to achieve ExTemp-hardened GaN electronics with improved performance and reliability.