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This paper presents an X-band bi-directional T/R chipset in 0.13 m CMOS. The T/R chipset consists of a bi-directional gain amplifier (BDGA), a 5-bit digital step attenuator with two BDGAs for compensating the switch losses, and a 6-bit phase shifter using DPDT switches. The phase and attenuation coverage is 360 with the LSB of 5.625°, and 31 dB with the LSB of 1 dB, respectively. The circuit has a reference state gain of >;3.5 db, and the return losses of >;11 db at 8.5-10.5 GHz. The T/R chipset has a phase shift accuracy with the RMS phase error of <;4.3°, while the RMS amplitude error is <;0.8 db at 8.5-10.5 GHz. The attenuation accuracy is measured to be db, while the RMS phase error is <;7.4° at 8.5-10.5 GHz. The output P1dB of the T/R chipset is >;6.5 dBm and the noise figure is <;7.5 db at 8.5-10 GHz. The chip size is 2.06 × 0.58 mm2 including pads, and the DC power consumption is 154 mW only in the BDGAs. To authors' knowledge, this is the X-band CMOS T/R chipset with the competitive RF performance compared to other device technologies, which has the smallest size and the lowest power consumption to-date.