We fabricated 50-nm-gate InAlAs/InGaAs high electron mobility transistors (HEMTs) lattice-matched to InP substrates using a conventional process under low temperatures below 300°C, and measured DC and RF performance. The measured cutoff frequency f _T of our 50-nm-gate HEMT is 362 GHz, which is the highest value ever reported for any transistor, and is much higher than the values reported for previous 50-nm-gate lattice-matched HEMTs. The excellent RF performance of our HEMTs might result from the low-temperature fabrication process.