A noninvasive energy-efficient FM-UWB transmitter is implemented in 65nm CMOS for stereo hearing aid applications. Different form the conventional FM-UWB transmitter, the proposed transmitter employs an 8-FSK subcarrier modulation method to enhance data rate by three times with slight increment of hardware complexity. The 8-FSK subcarrier modulation is achieved by a fast-settling PLL along with a pre-tuned relaxation VCO. The FM-UWB signal generated by an FLL-assisted ring VCO and a single-stage class AB power amplifier meets the FCC spectrum mask. The 3.5-4GHz 750kb/s transmitter consumes 1.14mW from a 1V supply, achieving an energy efficiency of 1.5nJ/bit.