Abstract In this paper, a 2K6 GHz wideband GaN power amplifier MMIC is designed and fabricated using a second-order all-pass filter for input impedance matching and an LC parallel resonant circuit for minimizing an output reactance component of the transistor. The second-order all-pass filter used for wideband lossy matching is modified in an asymmetric configuration to compensate the effect of channel resistance of the GaN transistor. The power amplifier MMIC chip that is fabricated using a 0.25 μm GaN HEMT foundry process of Win Semiconductors, Corp. is 2.6 mm×1.3 mm and shows a flat linear gain of about 13 dB and input return loss of larger than 10 dB. Under a saturated power mode, it also shows output power of 38.6K39.8 dBm and a power-added efficiency of 31.3K43.4 % in 2 to 6 GHz.Key words: GaN, HEMT, Power Amplifier, MMIC, Lossy Matching, All-Pass Filter M| 7:Q5 |S /+ 6IQ Q|f|z`X .. 82;[Q(Department of Radio Science and Engineering, Chungnam National University) LManuscript received May 26, 2015 ; June 24, 2015 ; Accepted June 30, 2015. (ID No. 20150526-039)LCorresponding Author: Dong-Wook Kim (e-mail: dwkim21c@cnu.ac.kr)