This article presents a K-band reconfigurable 4 x 4 balanced high power amplifier (HPA) adopting voltage-controlled phase inverters which can precisely provide relative phase shifts of 0 degrees and 180 degrees. By properly adjusting the relative phases in the 4 x 4 array paths of the proposed structure, a fixed input-to-output port relationship of the conventional balanced PA can be overcome through the improvement in output flexibility. The proposed 4 x 4 balanced HPA is configured by four K-band HPA microwave monolithic integrated circuits (MMICs), four phase inverter MMICs, and two 4 x 4 waveguide-Butler matrices as input and output passive networks. Each K-band HPA is fabricated with 0.15-mu m pHEMT process and has the size of 4.26 x 2.35 mm(2).