The effects of drain-source distance and applied voltage on low-frequency noise behavior of AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect-transistors incorporated with a photochemical vapor deposited (photo-CVD) SiO2 gate oxide layer were investigated. According to our studies, the normalized noise power density is inversely proportional to L' (=Ld-s - L-gate) when devices are biased in the linear region. However, the drain-source distance alone exerts little influence on low-frequency noise in the saturation and cutoff regions. Furthermore, the 1/f(Gamma) noise characteristics and the Gamma value were affected by the interface state distribution in the energy bandgap as the gate bias was varied. The normalized noise power density determined is independent of the drain-source voltage in the linear region, but it exhibits an enhancement in the saturation region in response to an increase in the drain-source voltage. However, the noise power density then becomes constant when devices are biased in the cutoff region. (c) 2006 The Electrochemical Society.