This thesis proposes an ultra-compact and reconfigurable X-band control MMIC, consisting of a SPDT switch, a 5-bit digital phase shifter and a 5-bit digital attenuator, for 5G phased array transceivers based on the 0.15-um GaN HEMT process. To ensure this work is fabrication-driven design, characterization of the fabricated GaN HEMTs, in which it shows the agreements between the design kit model and measurement results, is illustrated first. The SPDT switch has achieved an insertion loss of 0.65 dB and an isolation of 24.8 dB over 8-12 GHz with a IIP3 of 41 dBm. The 5-bit digital phase shifter has achieved an RMS phase and amplitude error of 9.9o and 6.5 dB. The 5-bit digital attenuator has achieved an RMS amplitude and phase error of 0.7 dB and 6o. Layout dimensions indicate the proposed control MMIC occupies an area size of 2 mm × 4 mm including RF and DC pads.