0.15 μm gate-length InP-based In0.52Al0.48As/In0.53Ga0.47As high electron mobility transistors (HEMTs) were successfully fabricated with gate-width of 2×50 μm and source-drain space of 2 μm. The maximum extrinsic transconductance (gmext) of 1 052 mS/mm was obtained under gate-source voltage (VGS) of 0.1 V and drain-source voltage (VDS) of 1.7 V at room temperature. Transmission Line Method (TLM) measurements revealed the contact resistance of 0.032 Ω·mm and the specific contact resistivity of 1.03×10-7 Ω·cm-2 on linear TLM patterns. Thus, markedly enhanced gmext was achieved by the superb Ohmic contact and the short source-drain space for minimizing series source resistance. These devices also demonstrated excellent RF characteristics. The fT and fmax extrapolated using the S-parameters measured from 100 MHz to 40 GHz were 151 GHz and 303 GHz, respectively. The HEMTs were promising for millimeter-wave band integrated circuits.