A global physical/electromagnetic HEMT simulation approach, entirely in the frequency domain, is here described for microwave CAD applications. The frequency-domain Spectral Balance technique for the solution of steady-state nonlinear differential equations is applied to the moments of Boltzmann's Transport Equation for the analysis of the intrinsic, active part of the device, yielding a very simple formulation. A numerical electromagnetic solver in the frequency domain is used for the analysis of the extrinsic, passive embedding and access structure. The two analyses are coupled, and give a self-consistent, global description of the device. The frequency-domain formulation allows easy inclusion of frequency-dependent parameters of the semiconductor, and a natural extension to multitone analysis, without the need for cumbersome time-frequency transformations. The thechnique is applied to a Quasi-2-Dimensional (Q-2D) hydrodynamic modeling of the active device for simplicity, but is suitable for more comprehensive approaches as well. DC and small-signal microwave results up to 40 GHz are obtained for a 0.3-µm gate-length AlGaAs–InGaAs–GaAs pHEMT transistor, and compared to experimental data.