A K-band high conversion gain high efficiency frequency quadrupler using a GaAs E/D-mode pseudomorphic high electron-mobility transistor (PHEMT) technology is presented in this paper. The frequency quadrupler comprises two cascade frequency doublers. The frequency doubler employs a modified common-gate (CG)/common-source (CS) topology to enhance the second harmonic efficiently. The phase-shifter networks are utilized to improve the fundamental suppression. Between 22 and 27 GHz, the proposed frequency quadrupler features a conversion gain of higher than −1.2 dB with an input power of 0 dBm. The maximum conversion gain is 1.8 dB at 25.6 GHz with an efficiency of up to 5.7% and a power-added efficiency (PAE) of 2%. At 24-GHz output frequency, the maximum output 1-dB compression point (P1dB) and the output saturation power (Psat) are higher than 2 and 3 dBm, respectively.