In this paper, we have studied on the fabrication of GaAs-based pseudomorphic high electron mobility transistors (PHEMT's) for the purpose of millimeter-wave applications. To fabricate the high performance GaAs-based PHEMT's, we have developed unit processes, such as 0.1 μm Γ-gate lithography, silicon nitride passivation, and air-bridge process to achieve high performance of device characteristics. The DC characteristics of the fabricated PHEMT was measured at a unit gate width of 70 μm and 2 gate fingers, and showed a good pinch-off property (VP = -1 V) and a drain-source saturation current density (Idss) of 373.53 mA/mm. Maximum extrinsic transconductance (gm) was 522.4 mS/mm at Vgs = -0.3 V, Vds = 1.5 V, and Ids = 0.5 Idss. The RF measurements were performed in the frequency range of 1.0 ∼ 50 GHz. For this measurement, the drain and gate voltage were 1.5 V and -0.3 V, respectively. At 50 GHz, 9.2 dB of maximum stable gain (MSG) and 4.2 dB of S21 gain were obtained, respectively. A current gain cut-off frequency (fT) of 113 GHz and a maximum frequency of oscillation (fmax) of 180 GHz were achieved from the fabricated PHEMT with a 0.1 μm gate length.