🔼The name Semachiah in the Bible
The name Semachiah (or rather: Semachiahu) occurs only once in the Bible. He is mentioned among the gatekeeping descendants of Obed-edom of Levi (1 Chronicles 26:7). The wording seems to suggest that Semachiah is a son of Shemaiah, Obed-edom's first born, but on the other hand, he and Elihu are mentioned separately as "brothers" (friends? cousins?) of the actual sons of Shemaiah. It's also possible that the first mentioned sons of Semachiah are the actual gatekeepers that this paragraph aims to list, while their brothers Semachiah and Elihu aren't gatekeepers but some other kind of "men of valor".
🔼Etymology of the name Semachiah
The name Semachiah (or rather Semachiahu) consists of two elements. The first part of this name comes from the verb סמך (samak), meaning to lean or lay upon, or secondarily: to support or uphold:
The final bit of our name is יה (Yah) = יהו (Yahu) = יו (Yu), which in turn are abbreviated forms of the Tetragrammaton; the name of the Lord: YHWH.
For a meaning of the name Semachiah, NOBSE Study Bible Name List has Yahweh Supports, Jones' Dictionary of Old Testament Proper Names reads Sustained Of The Lord, and BDB Theological Dictionary proposes Yah Has Sustained.