A GaInP/GaAs HBT micromixer for 2.4/5.2/5.7-GHz multiband WLAN applications is demonstrated. Our experimental results show that the input return loss |S11| is below -25 dB from DC to 10 GHz with power-conversion gains of 11.7, 11.9, and 11.5 dB at frequencies of 2.4, 5.2, and 5.7 GHz, respectively. The wideband matching characteristic makes the micromixer very suitable for multiband applications. Input P1dB is -4 dBm and IIP3 is 2.36 dBm. Port-to-port isolation is also quite satisfactory. In addition, the single-to-differential input stage in the Gilbert micromixer eliminates the need for common-mode rejection.