The present invention provides for a voltage-controlled crystal oscillator (VCXO) which, other than the crystal itself, is full integrated. The VCXO has a pre-amplifier block, a gain stage, a first MOS transistor, a first capacitor, a second MOS transistor, and a one second capacitor. The pre-amplifier block receives an input tuning voltage and the gain stage is connected across the terminals of the oscillating crystal. The first MOS transistor and first capacitor are connected between one of the terminals of the oscillating crystal and a reference voltage. The second MOS transistor and the second capacitor are connected between the second crystal terminal and the reference voltage. The gates of both MOS transistors are connected to the output node of the pre-amplifier block. The first and second MOS transistors connect the first and second capacitors to the first and second terminals of the gain stage for a portion of the time responsive to the input tuning voltage. Thus the oscillating crystal has a load capacitance, which varies according to the input tuning voltage, so that the frequency of the VCXO varies according to the input tuning voltage.