- The document summarizes key concepts about intrinsic and extrinsic semiconductors. - It defines intrinsic semiconductors as undoped semiconductors where the number of electrons and holes are equal. Current in intrinsic semiconductors is caused by both electron and hole flow. - Extrinsic semiconductors are doped, causing an imbalance between electrons and holes. N-type are doped with donor atoms, increasing free electrons. P-type are doped with acceptor atoms, increasing holes.