The 2000 Nobel Prize in Chemistry was given to three professors (Alan MacDiarmid, Alan Heeger, and Hidecki Shirakawa) who discovered that a special type of polymer could be made to conduct electricity.
These polymers are known as conjugated polymers.
All conjugated polymers have an alternating single bond - double bond structure along the backbone of the chain.
This alone makes them semiconductors.
The adding of free charge carriers, or doping, onto the chains increases the conductivity many orders of magnitude - into the range of common metals.
These materials are often referred to as synthetic metals.
I'll add more detail in additional writeups as I have time.