A 12-bit 2.6 GS/s radio frequency digital to analog converter (RF DAC) based on 1 μm GaAs heterojunction bipolar transistor (HBT) process is presented.The DAC integrates a 4∶1 multiplexer to reduce the data rate of input ports,which greatly facilitates the application.DAC core adopts 4 + 8 segmented current steering structure.R-2R ladder network is used for 8 least significant bit (LSB) to realize binary current weighting and thermometer coding is used for 4 most significant bit (MSB).Return-to-zero (RZ) technology is used to expand the effective bandwidth of DAC output to the third Nyquist band.The proposed DAC has a better output power flatness and spurious-free dynamic range (SFDR).Compared to traditional DAC,measured results demonstrate that the output power of this RZ DAC is increased by 33 dB and the SFDR is enhanced by 27 dB near the second Nyquist band.