A 2.4-GHz energy-efficient transmitter (TX) which supports multiple modulation schemes is reported. The proposed TX is based on the phase-selector architecture, where the modulation signal is generated by interpolating among quadrature phases at RF. This TX demonstrates the capability of supporting various PSK (OQPSK, HS-OQPSK, and 8-PSK) and the 16-QAM modulations. Fabricated in a 90-nm CMOS process, the TX consumes 8.9 mW and 13.8 mW at PSK and QAM modes, respectively. The maximum data rate is 105 Mbps under -3 dBm output power and 10.6 % EVM.