Abstract: A field-effect transistor (FET) for use at microwave frequencies has electrodes which act as transmission lines. Gate electrodes can comprise a narrow operative part between the source and drain electrodes which provides gating action, and a gate supply part which lies outside the source and drain electrodes and is connected to the operative part by a plurality of connections distributed along its length. In one form the device can be used as an amplifier and as such is capable of providing higher power handling capacity than conventional FETs, since the device can be extended in size and phase differences between various parts of the device compensate for one another. Other forms and applications are disclosed as a modulator and as a convoluter.