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It has recently been shown that, in addition to parasitics, the dipole domain which forms in FET-type devices produces a complex conjugate pole-pair which leads to a 12dB/octave gain roll-off in the millimetre-wave region. As a result the actual Fmax of millimetre-wave transistors is considerably less than that determined from the commonly used extrapolation of microwave frequency gain measurements at 6dB per octave roll-off. Here device models are used to compare the millimetre-wave performance of state-of-the-art MESFET, MODFET and PBT transistors. A parametric study indicates that frequency performance is particularly sensitive to drain parasitics.