Abstract: A semiconductor element having a MOS-capacitor between a zone provided in an epitaxial layer on a substrate and a conductive layer on an insulating layer above the zone is utilized in a structure comprising a tunable oscillator having a differential amplifier, a current distributor controlled by a control voltage, a phase shifting element comprising the MOS-capacitor and a feedback path present between the phase shifting element and an input of the differential amplifier. The feedback path comprises a quartz oscillator and an emitter-follower transistor. The stray capacitance between the zone and a substrate of the opposite conductivity type is considerably reduced by a further zone of the opposite conductivity type which is applied to a fixed potential through a connection electrode. This connection point is for the supply voltage of the circuit, while the further zone of the first conductivity type is connected parallel to the emitter-base current path of the emitter-follower transistor.

Abstract: A semiconductor element having a MOS-capacitor between a zone provided in an epitaxial layer on a substrate and a conductive layer on an insulating layer above the zone.The stray capacitance between the zone and the substrate of the opposite conductivity type is considerably reduced in that the zone in the semiconductor body is surrounded by a further zone of the opposite conductivity type. The further zone may be applied to a fixed potential via a connection electrode.