Voltage-sensitive resistors which utilize the inherent properties of semiconductor junctions to achieve useful non-linear properties are generally referred to in the United States as diodes or varistors. Which term is chosen depends on the symmetry of the voltage/current characteristic of the device. If it is non-symmetrical with respect to the origin of the co-ordinate axes, it is a diode; if it is symmetrical, it is a varistor.The paper presents the electrical and thermal characteristics, as well as the general method of fabrication, of a variety of diodes and varistors which have been developed over the past five years. Included are devices intended for use as regulators, limiters (both fractional-voltage and multiple-voltage), surge and lightning protectors, modulators and demodulators, and voltage references. Comparisons are made between voltage-sensitive resistors made from copper oxide and silicon carbide and new devices, particularly those made by diffusion techniques in silicon.For critical voltage-reference applications, diodes have been developed which have extremely low temperature coefficients, comparable to the best standard references now available. A description of these, and of the reliability of semiconductor diodes in general, is also given.