They are useful for jobs like coating electric wires to prevent them from 'shorting together' or giving you a shock. Insulators are also very useful to fill the 'gap' in between the metal plates of a capacitor. Semiconductors All the transistors, diodes, integrated circuits, etc. The basic property of a semiconductor is given away by its name - it 'conducts a little bit'. A semiconductor will carry electric current, but not as easily as a normal conductor.
Some materials are intrinsic semiconductors.
The semiconducting properties occur in these materials naturally. However, most of the semiconducting materials used in electronics are extrinsic . This means that left to themselves they are excellent insulators. These materials are turned into semiconductors by doping them with small amounts of foreign atoms. The number of doping atoms you need to add is very small.