Silicon (Si) and germanium (Ge) are well-known semiconductor materials. When they are pure crystals, these substances are close to insulators (intrinsic semiconductors), but doping a small amount of dopant causes the electrical resistance to drop greatly, turning them into conductors.
Depending on the kind of dopant, n-type or p-type semiconductor can be made.
Semiconductors made of several elements are called compound semiconductors, as opposed to those made of a single element such as silicon semiconductors. There are combinations such as Group III and Group V of the periodic table, Group II and Group VI, Group IV, etc.