CBSE Class 12 · 2015 · Delhi · SemiconductorsShort Answer

An intrinsic semiconductor is a pure crystal in which conduction is only by thermally generated electron-hole pairs, so $n_e=n_h$ and the conductivity is small.
An extrinsic semiconductor is formed by doping with impurity atoms; one type of carrier dominates ($n_e\ne n_h$) and the conductivity is much higher and can be controlled by the doping level.
$\boxed{\text{Intrinsic: pure, }{n}_e=n_h;\text{Extrinsic: doped, }{n}_e\ne n_h.}$