What is the characteristic of a substance identified as a semiconductor?

A semiconductor is characterized by its ability to exhibit properties between those of conductors (like metals) and insulators (like non-metals). This unique behavior is evident in its electrical conductivity, which can vary widely based on external factors such as temperature, impurities (doping), and the presence of electric fields. In contrast to conductors, where conductivity remains relatively high, semiconductors possess a conductivity that is lower than that of metals but higher than that of typical insulators.

The concept of semiconductors being able to act as either conductors or insulators makes them valuable in electronic applications. For instance, at low temperatures, semiconductors often behave like insulators, while at higher temperatures or when doped with certain impurities, their conductivity increases significantly, allowing them to conduct electricity.

The other options highlight misunderstandings about semiconductors. They do not have infinite conductivity; this characteristic is exclusive to ideal conductors. Likewise, semiconductors do not act solely as conductors, as their ability to behave like insulators is a fundamental aspect of their function in electronic devices.