Semiconductor elements like silicon and germanium have 4 electrons in their valence band and when highly purified and doped with tiny amounts of elements having either 3 electrons or 5 electrons in their valence band the electrical properties can be very precisely controlled and microscopic components (e.g. transistors, diodes, resistors, capacitors) can be made.Silicon has a couple of advantages over germanium making it more practical to use:Silicon will function up to 150C, but germanium will only function up to about 60C.Silicon's oxide is a stable insulator, but germanium's oxide is crumbly and water soluble. This facilitates the use of silicon to make integrated circuits containing many billions of microscopic components that can be packaged many ways including in molded plastic cases. Germanium is really not practical to make anything but individual discrete transistors or diodes with and they must be packaged in hermetically sealed metal or glass cases.Diamond or carbon nanotubes may someday be practical as semiconductors, especially since they should function up to 600C but this will take much research effort before they are ready for market.