Abstract: A Ku-band 6 bit digital attenuator of microwave monolithic integrated circuit (MMIC) was developed based on GaAs E/D pseudomorphic high electron mobility transistor (pHEMT) process. The 6 bit digital attenuator was made up of six base states. It could obtain maximum attenuation of 31.5 dB with the attenuation step of 0.5 dB. 0.5 dB and 1 dB attenuation bits were realized by adopting simplified T-type structure. In the 16 dB attenuation bit, a switched-path-type topology was employed to improve the attenuation flatness and reduce the additional phase shift effectively. The measurement results show that in the range of 12−18 GHz, the 64-state root mean square (RMS) error is less than 0.25 dB, the phase variation is from −0.5° to ＋9.5°, the insertion loss is less than 4.9 dB and the input and output voltage standing wave ratios are both less than 1.5∶1. The chip size is 3.00 mm×0.75 mm. The MMIC chip has the characteristics of wide bandwidth, high attenuation accuracy and small size. It can be mainly used in fields such as microwave phased array radar transceiver components and communication.