Aiming at the specific protocol of RFID technology, a 915 MHz CMOS transmitter front-end for OOK modulation is implemented in a 0.18 μm CMOS process. The transmitter incorporates a class-E power amplifier (PA), a modulator, and a control logic unit. The direct-conversion architecture minimizes the required on-and-off-chip components and provides a low-cost and efficient solution. A novel structure is proposed to provide the modulation depth of 100% and 18% respectively. The PA presents an output 1 dB power of 17.6 dBm while maintaining a maximum PAE of 35.4%.