A favourite given-name character for its 'bright and thriving' meaning, as in the Tang general 李晟. The same brightness sense is also read 晟 by some, and as a surname it is read 晟 - but shèng is the standard reading.
The sun radical 日 sits on top. It directly supplies the meaning: 晟 is the blazing brightness of the sun, the source of its 'brilliant, flourishing' sense.
The lower part 成 supplies the sound - its reading survives in the alternate pronunciation 晟 and shifted to shèng in the standard reading. The shared phonetic also links to 盛 'flourishing', echoing this character's meaning.
