At what temperature does a semiconductor start to conduct electricity effectively?

Semiconductors begin to conduct electricity effectively at around room temperature, typically between 25°C to 30°C. This is because, at these temperatures, the thermal energy being supplied to the semiconductor is sufficient to excite electrons across the energy band gap, allowing them to move freely and contribute to electrical conduction.

At lower temperatures, such as 0°C or below, the semiconductor remains in a less conductive state due to reduced thermal energy, which limits the excitation of electrons. Similarly, at -20°C, the conductivity is significantly low as the thermal energy is not adequate to promote the necessary electron transitions.

While certain semiconductors might exhibit conductivity at elevated temperatures (like 100°C), they generally do not reach effective conduction levels until they approach room temperature. Therefore, around room temperature is optimal for typical semiconductor materials to operate effectively, making it the correct choice.