A wireless biotelemetry system operates in vivo, which requires low power consumption for long-lasting operation, high output power for long transferable distance, and high throughput for incorporating many recording electrodes and transmitting raw brain signals. An implantable 2.4-GHz on-off keying (OOK) transmitter with high throughput and high energy efficiency for wireless biotelemetry systems has been designed in a 0.18-μm CMOS process. To balance power consumption and output power, a complementary voltage-controlled oscillator for the proposed transmitter is employed. Power consumption of the transmitter is reduced by switching the oscillator on and off to generate an OOK modulated signal. The transient delay for the transmitter is derived and applied to implement a high throughput transmitter. Rat skin-mimic emulating the implant environment such as electrical properties of the skin is used to measure the proposed transmitter in vitro. To transmit 136 Mb/s of OOK data, the transmitter consumes 3 mW of dc power and generates an output power of -14 dBm. The transmitter achieves energy efficiency of 22 pJ/bit with an associated bit error rate of 1.7 × 10- 3 without using an error correction scheme.