In this paper, a 5-GHz fully integrated voltage-controlled oscillator (VCO) using an InP-based RTD/HBT technology is demonstrated for the first time. A figure of merit for the oscillator is obtained to be - 180.8 dBc/Hz. In addition, the VCO has demonstrated a wide tuning range of 710 MHz at 5 GHz. (c) 2005 Wiley Periodicals, Inc.