A fully integrated up-conversion double balanced mixer for 802.11a application is designed and fabricated by using InGaP/GaAs HBT process. Fabricated mixer shows high linearity due to high linearity characteristic of InGaP/GaAs HBT and passive output balun. For single-ended input and single-ended output configuration, RF/LO/EF baluns are all integrated on a chip and no off-chip component has been used. Active baluns for EF/LO baluns and a passive balun for RF balun are used respectively. A LC current combiner technique which is consisted of high Q on-chip inductors and a capacitor is used for a passive RF balun. Fabricated chip consumes 5 mA currents for mixer core and uses 3 V supply voltage. Chip size is 1.0 mm * 1.17 mm. The measured performance is 3.7 dB power conversion gain, -8 dBm P1dB, 3 dBm OIP3, 30 dB LO-RF isolation, when input IF signal power is -16 dBm and LO signal power is -14 dBm.