A solid state Klystron structure is fabricated by forming a source contact and a drain contact to both ends of a conducting wire and by forming a bias gate and a signal gate on the conducting wire. The conducting wire may be at least one carbon nanotube or at least one semiconductor wire with long ballistic mean free paths. By applying a signal at a frequency that corresponds to an integer multiple of the transit time of the ballistic carriers between adjacent fingers of the signal gate, the carriers are bunched within the conducting wire, thus amplifying the current through the solid state Klystron at a frequency of the signal to the signal gate, thus achieving a power gain.