A 164 GHz source in a hetero-integrated semiconductor technology is presented. It features a fundamental frequency voltage-controlled oscillator in BiCMOS, which is used to drive a doubler-amplifer chain in transferred-substrate InP-HBT technology, integrated on top of the BiCMOS wafer in a wafer-level Benzocyclobutene based bonding process. The VCO operates at 82 GHz with an output power of approximately 8 dBm. The combined circuit delivers 0 dBm at 164 GHz. Measured output power agrees well with simulations. The results demonstrate the feasibility of hetero-integrated circuits operating well above 100 GHz.