This article presents a rigorous investigation of the electrical transport dynamics of GaAs devices at high temperatures up to 900°C with terahertz (THz) spectroscopy techniques. Results revealed a significant decrease in THz transmission above 400°C for the GaAs device due primarily to a thermally activated surge in carrier density. The investigation also revealed the evolution of transient THz complex photoconductivity over time and temperature to be in good agreement with the Drude model. This investigation demonstrates the feasibility of applying THz spectroscopy to accurately characterize the critical physical performance of other semiconductors for high-temperature electronic and photoelectronic applications.