This paper presents a power-efficient, high data rate QPSK transmitter for wireless biomedical applications at the frequency of 430MHz. The transmitter architecture is based on a sub-harmonic injection-locked voltage-controlled oscillator (VCO) and the phase modulation is realized by directly modifying the VCO self-resonant frequency. A single-ended Class-E power amplifier (PA) is adopted in the transmitter with an efficiency of 46% (including pre-driver). Implemented in 0.18μm CMOS technology, the proposed transmitter consumes 5.8mw with 20Mbps data rate and 0.11dBm output power.