This paper presents a completely integrated, low-power 6.3 GHz oscillator transmitter which includes an on-chip antenna suitable for short-range medical sensor applications. The transmitter, implemented in a 1.2 V 0.13 mum CMOS process, utilizes open-loop direct VCO modulation for BFSK data at a rate of 300 kbps. For communicating a 1 kbit packet once per second, an average power consumption of 14 muW is achieved. During a packet transmission, the power consumption of the transmitter is 4.25 mW, enabling a self-powered design using integrated ultracapacitors for an SoC solution. With a radiated power of 0 dBm, the transmitter has a communication range of 2 m.