What is a covalent semiconductor?
No, most semiconductors are ionic.

I'm not sure I've seen the term "covalent semiconductor" before. Wikipedia has an article on covalent superconductors.

I think the main point would be that many if not most semiconductors are inorganic solid-state compounds. Consequently, most of these (e.g. III-V semiconductors are ionic solids, not really covalent ones. Consider GaAs or InP, which are typically classified as ionic.

That is the solid state electronic structure can be considered mainly composed of cations and anions (unlike organic chemistry where the electronic structure is considered mainly of neutral atoms).

(Incidentally, defining whether some of these compounds have purely ionic or purely covalent interactions is somewhat futile, since most bonding interactions are both somewhat ionic and covalent.)