Which description best defines a thermistor?

• A. A resistor made of metal film.
• B. A capacitor with humidity dependence.
• C. A diode whose current varies with voltage.
• D. A resistor made of semiconductor material whose resistance varies with temperature.

Answer: (D)

Thermistors are temperature-sensitive resistors made from semiconductor materials. Their resistance changes with temperature far more than ordinary metal resistors, which is why they’re used for sensing and temperature compensation. There are two main types: NTC, where resistance drops as temperature rises, and PTC, where resistance rises with temperature. This nonlinear, temperature-dependent resistance is the defining feature.

The other descriptions don’t fit: metal film resistors aren’t defined by large temperature sensitivity; a humidity-dependent capacitor is a different sensor family; and a diode’s behavior is tied to its junction, not a resistance that tracks temperature. So the description that matches a thermistor is a resistor made of semiconductor material whose resistance varies with temperature.