In metals and most common conductors, yes, electrical resistance increases with temperature. But the full answer depends on the material. Semiconductors, electrolytes, and superconductors all behave differently, and understanding why gives you a much clearer picture of how electricity actually works.
Why Metals Resist More at Higher Temperatures
Metals are the straightforward case. Their atoms are arranged in a repeating crystal lattice, and electrons flow through that lattice like cars on a highway. At higher temperatures, the atoms vibrate more energetically around their fixed positions. These vibrations (called phonons in physics) act like obstacles, scattering the electrons and disrupting their flow. The hotter the metal, the more violent the vibrations, and the harder it is for electrons to move in an orderly way through the material.
In a high-purity metal, this vibration-based scattering dominates at all but the lowest temperatures. Impurities, grain boundaries, and other structural defects also scatter electrons, but in clean metals at room temperature, thermal vibration is the main source of resistance. This is why a copper wire at 100°C conducts noticeably worse than the same wire at 20°C.
How Much Resistance Changes in Common Metals
The relationship between temperature and resistance in metals is nearly linear over normal temperature ranges. Engineers use a value called the temperature coefficient of resistance to quantify it. For copper at 20°C, this coefficient is approximately 0.00393 per degree Celsius. That means for every 1°C increase, copper’s resistance rises by about 0.4%. Over a 50-degree swing, that adds up to roughly a 20% increase in resistance.
Other common metals behave similarly. Aluminum has a comparable temperature coefficient, and gold follows the same general trend. The exact values shift depending on the purity and physical form of the metal. Thin films of gold or aluminum, for instance, can have slightly different coefficients than bulk material. But the direction is always the same: hotter metal, higher resistance.
Why Semiconductors Work in Reverse
Semiconductors like silicon and germanium behave oppositely to metals, at least at moderate to high temperatures. Their resistance typically decreases as temperature rises. The reason comes down to how these materials produce the charge carriers (free electrons and “holes”) that allow current to flow.
In a semiconductor, electrons are normally locked in bonds between atoms. They need a small push of energy to break free and enter the conduction band, where they can actually carry current. Heat provides that energy. As the temperature climbs, more electrons absorb enough thermal energy to jump into the conduction band, and each freed electron also leaves behind a hole that acts as a second charge carrier. This flood of new carriers overwhelms the increased scattering from lattice vibrations, so overall resistance drops.
At very high temperatures (above roughly 127°C for many semiconductors), the thermally generated carriers dominate completely, and conductivity increases exponentially with temperature. This is why semiconductor-based temperature sensors are so sensitive to small changes in heat.
Superconductors: Resistance Drops to Zero
At the extreme cold end of the spectrum, certain materials lose all electrical resistance entirely. Mercury was the first material found to do this, dropping to zero resistance below 4.1 K (about -269°C). Since then, dozens of superconducting materials have been identified, each with its own critical temperature where resistance vanishes.
Common superconductors and their critical temperatures span a wide range:
- Aluminum: 1.2 K
- Tin: 3.7 K
- Lead: 7.2 K
- Niobium: 9.5 K
High-temperature superconductors discovered in the 1980s pushed these thresholds much higher. Yttrium-barium-copper-oxide becomes superconducting at 92 K, and thallium-based compounds reach 125 K. These can be cooled with liquid nitrogen (which boils at 77 K), making them far more practical than materials requiring liquid helium.
Electrolytes Follow Their Own Rules
Liquids that conduct electricity through dissolved ions, such as saltwater or battery electrolytes, also see resistance decrease with temperature. The mechanism is different from semiconductors. In an electrolyte, ions carry the current instead of electrons, and their ability to move depends on how easily they can push through the surrounding liquid. Higher temperatures reduce the viscosity of the solvent, letting ions move faster and more freely. The result is lower resistance.
This is why batteries perform poorly in extreme cold. The electrolyte becomes more viscous, ion mobility drops, and internal resistance climbs. In hot conditions, the opposite happens: ions flow more easily and resistance falls, though excessive heat can degrade the battery through other mechanisms.
How This Plays Out in Real Life
The temperature-resistance relationship has direct consequences for electrical infrastructure. Power transmission lines are made of aluminum and copper, both of which lose efficiency as they heat up. On hot summer days, the lines themselves get warmer from both ambient heat and the current flowing through them, increasing resistance and wasting more energy as heat. This creates a feedback loop: higher resistance generates more heat, which raises resistance further. The Pacific Northwest National Laboratory has flagged this as a growing concern for grid reliability during extreme heat events.
Engineers also exploit the temperature-resistance relationship deliberately through components called thermistors. A negative temperature coefficient (NTC) thermistor decreases in resistance as it warms up, making it useful as a temperature sensor or an inrush current limiter that gradually allows more current as it heats. A positive temperature coefficient (PTC) thermistor increases in resistance above a specific switching temperature, which makes it work as a resettable fuse. If a circuit draws too much current, the PTC thermistor heats up, its resistance spikes, and current flow drops to safe levels. Once it cools, it resets automatically.
The bottom line: resistance increases with temperature in metals, decreases in semiconductors and electrolytes, and drops to zero in superconductors below their critical temperature. The type of material determines the direction, and the underlying physics in each case is different.