The high linearity downconversion active mixers are demonstrated in the horizontal current bipolar transistor (HCBT) technology. The HCBTs fabricated by uniform n-collector doping profile, long hydrofluoric (HF) etching, and long tetramethylammonium hydroxide (TMAH) etching are shown to be optimal for mixer performance. The circuits fabricated with the optimum HCBTs in 180-nm bipolar complementary metal-oxide semiconductor (BiCMOS) process are packaged and measured, resulting in the best HCBT mixer characteristics published so far. The HCBT mixer uses a double-balanced Gilbert cell core with an integrated local oscillator (LO) buffer driver and employs an open-collector output topology. It provides broadband operation and frequency downconversion, measured up to 3 GHz, with a maximum power consumption of 550 mW at the peak linearity performance. The measured peak input third-order intercept point (IIP3) and conversion gain (CG) of 30.3 dBm and 6.0 dB, respectively (at 900-MHz input), are suitable for the base station transceivers and wireless infrastructure. The HCBT technology represents a low-cost BiCMOS platform capable of meeting the various requirements in the fabrication of the radio frequency integrated circuits (RFICs).