This paper presents an energy-efficient sensor node transmitter for body channel communication (BCC) system. The OFDM modulation is adopted in this work to achieve both high transmission data rate and spectrum efficiency. To reduce the power dissipation of the front-end (FE) circuits, a phase-modulated outphasing architecture is applied to avoid the power-hungry data converters and linear amplifier. Besides, the voltage scaling and balanced source gating (BSG) schemes are proposed to save the circuit active power, resulting in 81.3% reduction. The proposed sensor node transmitter chip is manufactured in 90 nm standard CMOS process with a die area 1.1016 mm 2. The proposed BCC system is operated at 40 / 80 MHz with 10 MHz signal bandwidth, and the maximum data rate of 14.55 Mbps with 0.67 mW power dissipation can be achieved, leading to 0.05 nJ/b transmission energy and 1.46 bps/Hz spectral efficiency.