semifinalist vs competitor

semifinalist and competitor both are nouns.

Word	Noun	Adjective	Verb	Adverb
semifinalist	Yes	No	No	No
competitor	Yes	No	No	No

As nouns, competitor is a hypernym of semifinalist; that is, competitor is a word with a broader meaning than semifinalist:

semifinalist: one of four competitors remaining in a tournament by elimination
competitor: the contestant you hope to defeat

Other hypernyms of semifinalist include challenger, competition, contender, rival.

semifinalist (noun)	competitor (noun)
one of four competitors remaining in a tournament by elimination	the contestant you hope to defeat