a condenser in the form of a semiconductor diode whose capacitance depends nonlinearly on the voltage applied to it. This capacitance is the barrier capacity of the p-n junction; it varies from a few to hundreds of picofarads (in certain variable-capacitance diodes, virtually by a factor of 3-4) in case of variations of several dozen volts in the reverse (negative-sign) current. Varicaps have high efficiency (minor losses of electrical energy) and a low temperature coefficient of capacitance, independence of frequency in virtually the entire range of radio frequencies, and stability of parameters with time. Varicaps are manufactured from silicon, germanium, and gallium arsenide. In radio and electronic equipment, the characteristic of nonlinear variation of capacitance in varicaps is used to obtain parametric amplification and frequency multiplication, and the possibility of electrical control of the capacitance value is used for remote and noninertial tuning of the resonance frequency of oscillatory circuits.