A vowel-like sound which functions in a consonant-like way as the onset or coda of a syllable. The semivowels of Spanish are [j] and [w].

Semivowels (also glides, more rarely: semiconsonants) are non-syllabic vowels that form diphthongs with syllabic vowels. They may be contrasted with approximants, which are similar to but closer than vowels or semivowels and behave as consonants. Semivowels are normally written by adding the IPA non-syllabic mark to a vowel symbol, but often for simplicity the vowel symbol alone is written.