Where does “ש־מ־ע” come from?

ש־מ־ע (Hebrew) comes from Proto-Semitic *šamaʕ-.

Ancestry of “ש־מ־ע”, step by step

Step	Language	Word	Meaning
1	Proto-Semitic	*šamaʕ-	—

ש־מ־ע — Etymology, Origin & Word History | Etymology Explorer