Final answer:
Tellurium (Te) is the element that fits the description as a metalloid used in semiconductors and is not malleable.
Step-by-step explanation:
The element that best fits the description provided is Tellurium (Te). Tellurium is part of the metalloid family, with properties of both metals and nonmetals. Metalloids like tellurium have semiconductor properties, meaning they can conduct electricity but not as well as metals. Tellurium, along with other metalloids such as boron, silicon, germanium, arsenic, and antimony, can be found along the 'stair-step' line in the periodic table, which separates metals and nonmetals. Moreover, tellurium is known for not being malleable, aligning with the properties of nonmetals.