Abstract-In this paper, we present a multi-physics approach for the simulation of high-power RF and microwave transistors, in which electromagnetic, thermal, and nonlinear transistor models are linked together within a harmonic-balance circuit simulator. This approach is used to analyze a laterally diffused metal-oxide semiconductor (LDMOS) transistor that has a total gate width of 102 mm and operates at 2.14 GHz. The transistor die is placed in a metal-ceramic package, with bondwire arrays connecting the die to the package leads. The effects of three different gate bondpad layouts on the transistor efficiency are studied. Through plots of the spatial distributions of the drain efficiency and the time-domain currents and voltages across the die, we reveal for the first time unique interactions between the electromagnetic effects of the layout and the microwave behaviour of the large-die LDMOS power field-effect transistor (FET).Index Terms-Global modeling, electrothermal, laterallydiffused metal-oxide-semiconductor (LDMOS) transistor, power field-effect transistor (FET).

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