A traveling wave device employs an active Gallium Nitride FET. The Gallium Nitride FET has a plurality of gate feeding fingers connecting to an input gate transmission line. The FET has a drain electrode connected to an output drain transmission line with the source electrode connected to a point of reference potential. The input and output transmission lines are terminated with terminating impedances which are not matched to the gate and drain transmission lines. The use of Gallium Nitride enables the terminating impedance to be at much higher levels than in the prior art. The use of Gallium Nitride permits multiple devices to be employed, thus resulting in higher gain amplifiers with higher voltage operation and higher frequency operation. A cascode traveling wave amplifier employing GaN FETs is also described having high gain and bandwidth.