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This paper proposes a new design method for passive FET switches in the millimeter-wave (MMW) regime. In contrast to the conventional resonant-type switch design method, this passive FET switch circuit utilizes impedance transformation to compensate the drain-source capacitance effect for the off state at high frequencies. By means of this new design concept, a Q- and V-band monolithic-microwave integrated-circuit single-pole double-throw (SPDT) switches using a GaAs pseudomorphic high electron-mobility-transistor process are demonstrated. The Q-band SPDT switch has a measured isolation better than 30 dB for the off state and 2-dB insertion loss for the on state from 38 to 45 GHz, while the V-band switch also shows a measured isolation better than 30 dB for the off state and 4-dB insertion loss for the on state from 53 to 61 GHz. The obtained isolation performance using this design approach outmatches previously published FET switches in the MMW frequency range.