Low-frequency noise has been studied inAl0.15Ga0.85N/GaNhigh electron mobility transistors grown on sapphire substrates by metal organic vapor phase epitaxy. By varying the gate voltage(VGS),three regions of drain 1/f noise were clearly established underVDS=50&hthinsp;mVbiasing. FromVGS=−4&hthinsp;V(pinch-off) to 0 V, noise power generated at the transistor channel, which scales with device area, dominates. A Hooge parameter as low as5×10−4was found atVGS=0&hthinsp;V.ForVGS>0&hthinsp;V,noise power density does not depend on device area. At low gate voltages noise is generated at the ohmic contacts, whereas forVGS>1.25&hthinsp;Vit is related to the gate leakage Schottky current. A random telegraph signal (RTS) excess noise originating in the ohmic contacts has also been investigated by using a temperature analysis. ©1999 American Institute of Physics.