Abstract: A microwave oscillator using a transit-time transistor structure with a space charge zone, is provided. The negative resistance introduced by the transit-time in the space charge zone is utilized in a circuit connected with emitter and collector, the base being direct-biased and not passing the high frequency. To avoid a short-circuiting by the parasitic base-collector capacitance, a transmission line is connected in parallel across the base and collector terminals. The input impedance of this line is adjusted by short-circuiting this line at a distance close to a quarter of wavelength, thus creating an input inductance able to compensate the effect of the base-collector capacitance.