As gate-all-around field-effect transistors (GAAFETs) are scaled toward sub-10 nm gate lengths and nanowire diameters, self-heating effects (SHE) become an increasingly dominant reliability and performance concern, particularly for high-mobility III–V channel materials such as GaAs whose thermal conductivity is roughly three times lower than that of silicon. This paper reviews recent literature on self-heating in GAAFET architectures, presents the device structure and the coupled electro-thermal simulation methodology used to analyze a GaAs-channel nanowire GAAFET, and discusses the qualitative and analytical trends of temperature rise as a function of gate length, nanowire diameter, and the number of vertically stacked channels. The results indicate that geometric scaling, while beneficial for electrostatic control and short-channel immunity, systematically increases the thermal resistance of the device and therefore the magnitude of self-heating, an effect that is significantly more pronounced in GaAs than in Si.