Here's why:

* Unstable at Certain Temperatures: Germanium has a relatively low melting point (937.4 °C) compared to other semiconductors like silicon. At high temperatures, it can become unstable and its properties can change, making it less effective as a semiconductor.

* Reliable Semiconductor: Germanium was historically the first widely used semiconductor material. It exhibits excellent electrical conductivity properties at room temperature and is a good conductor of electricity, making it suitable for various electronic devices.

Note: Silicon (Si) is now the most commonly used semiconductor material due to its higher melting point and better stability at higher temperatures.

Let me know if you have any other questions!