This letter presents a high-efficiency 60-GHz CMOS transmitter for short-range wireless communications. The transmitter comprises a voltage-controlled oscillator and a modulator and uses on-off keying (OOK) modulation for a compact and low-power design. A frequency-doubling modulation technique produces a compact and highly efficient modulator with high on-off isolation. Therefore, the transmitter consumes low power and exhibits a high data-rate capability. Implemented in 65-nm CMOS technology, the transmitter consumes 12.2 mW and occupies a core chip area of 0.04 mm 2. The transmitter achieves 11.5-Gb/s wireless OOK data transmission over a distance of 2 cm at a bit error rate of less than 10(-12) for 2(7) - 1 PRBS. As a result, the proposed transmitter exhibits an energy efficiency of 1.1 pJ/b.