In this paper, DC and low-frequency noise characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) with different gate-to-source lengths (LGS) are presented. Due to the different (LGS), the device with shortest shows highest transconductance (gm) and drain current. But the threshold voltages (VTH) are the same for all devices. In low-frequency noise measurement, not only flicker noise (1/f noise) exists also accompany by generation-recombination noise (G-R) noise). Noise power spectral densities (PSD) are similar in devices with different LGS, and 1/f noise shows carrier number fluctuation (CNF) is the dominant cause. In addition, this paper discussed the G-R noise and extracted the traps in GaN buffer layer with activation energy of ∼ 0.35eV.