Here's why:

* Semiconductors are materials with electrical conductivity between that of a conductor (like copper) and an insulator (like glass). This means they can conduct electricity, but not as well as metals, and their conductivity can be controlled by factors like temperature and impurities.

* Semi-metals (also known as metalloids) are elements that have properties of both metals and non-metals. They are usually shiny and brittle, and can conduct electricity better than non-metals but not as well as metals.

While silicon and germanium share some properties with semi-metals, they are fundamentally classified as semiconductors due to their unique electrical conductivity characteristics.

Here's a breakdown of the key differences:

Semiconductors:

* Conductivity: Intermediate between conductors and insulators.

* Temperature Dependence: Conductivity increases with temperature.

* Impurity Dependence: Conductivity can be significantly altered by adding impurities (doping).

* Examples: Silicon, germanium, arsenic, gallium.

Semi-metals:

* Conductivity: Generally poor conductors, but better than non-metals.

* Temperature Dependence: Conductivity usually decreases with temperature.

* Impurity Dependence: Less sensitive to impurities than semiconductors.

* Examples: Boron, silicon, germanium, arsenic, antimony, tellurium, polonium.

While silicon and germanium are included in the list of semi-metals sometimes, their dominant characteristic is their semiconductor behavior, which makes them incredibly important for electronics and technology.