Semiconductors have conductivity properties between those of conductors and nonconductors.

Silicon is an example of a semiconductor. Cold semiconductors are poor conductors of electricity, but their conductivity rises when they are heated.

Small amounts of impurities often change the conductivity of semiconductors. Doped silicon is used to make the majority of computer chips today. 'Doped' implies that small amounts of some impurity (like phosphorous) has been added to enhance the silicon's conducting properties.

Doped silicon demonstration.