Abstract: A 6～18GHz 5 bit MMIC digital phase shifter was designed, using GaAs PHEMT technolog. High performance and yield of the product are obtained by making accurate models, choosing appropriate configuration, optimizing schematic and layout and especially using performance redundancy optimization strategy in the optimization process. The typical value of test electrical property shows that in the working frequency, the phase error of 11.25°/ 22.5° bit is less than 2.5°,the phase error of 45° / 90° /180° bit is less than 5°, RMS phase shift error is less than 4.5°, the insertion loss is restriction in the range of 7dB～10.5dB, input and output VSWR of 32 phase shift states is less than 1.7. The ultimate chip area is only 3.555mm×4.055mm×0.1mm. The chip could be widely used in phased array radar and electronic countermeasures engineering.