A semiconductor is a solid chemical element or compound, that can conduct electricity only under certain conditions. It is a good medium for supplying controlled electrical current. Its conduction varies depending on the current or voltage applied on it and the types of imputiry it doped with. Its conductivity is between an insulator and conductor. 

Semicondutors are used extensively in electrical circuits. Most common semiconductor materials are Silicon (Si) and Germanium (Ge). However Silicon is widely used for manufacturing semiconducting devices like diodes.