And if you checked further you'd find this:
http://en.wikipedia.org/wiki/Semivowel# ... ith_vowels
Semivowels, by definition, contrast with vowels by being non-syllabic. In addition, they are usually shorter than vowels. In languages as diverse as Amharic, Yoruba, and Zuni, semivowels are produced with a narrower constriction in the vocal tract than their corresponding vowels. Nevertheless, semivowels may be phonemically equivalent with vowels. For example, the English word fly can be considered either as an open syllable ending in a diphthong [flaɪ̯], or as a closed syllable ending in a consonant [flaj].
The definitional difference between a semivowel and a vowel is that the former are nonsyllabic, but this is only a required distinction if you deny the existence of open syllables.
Compare to this:
A syllabic consonant is a consonant which either forms a syllable on its own, or is the nucleus of a syllable.
Many dialects of English may use syllabic consonants in words such as even [ˈiːvn̩], awful [ˈɔːfɫ̩] and rhythm [ˈɹɪðm̩], which English dictionaries' respelling systems usually treat as realizations of underlying sequences of schwa plus consonant (e.g. /ˈiːvən/).
A number of languages have syllabic fricatives, also known as fricative vowels. In several varieties of Chinese, certain high vowels following fricatives or affricatives are pronounced as extensions of the sounds, with voicing added (if not already present) and a vowel pronounced while the tongue and teeth remain in the same position as for the preceding consonant, leading to the turbulence of a fricative carrying over into the vowel. In Mandarin Chinese, this happens for example with sī shī rī. Traditional grammars describing them as having a "buzzing" sound. A number of modern linguists describe them as true syllabic fricatives, although with weak frication. This is accordingly transcribed [sź̩ ʂʐ̩́ ʐʐ̩́] respectively.
So the distinction between semivowels and vowels is that vowels are the nucleus of a syllable, but sonorants as closed as fricatives can be used as syllable nuclei.
A diphthong (/ˈdɪfθɒŋ/ or /ˈdɪpθɒŋ/; Greek: δίφθογγος, diphthongos, literally "two sounds" or "two tones"), also known as a gliding vowel, refers to two adjacent vowel sounds occurring within the same syllable. Technically, a diphthong is a vowel with two different targets: that is, the tongue moves during the pronunciation of the vowel. For most dialects of English, the phrase "no highway cowboys" contains five distinct diphthongs.
Diphthongs contrast with monophthongs, where the tongue doesn't move and only one vowel sound is heard in a syllable. Where two adjacent vowel sounds occur in different syllables—for example, in the English word re-elect—the result is described as hiatus, not as a diphthong.
This is exactly what happens with the more open so called consonants.
How can we not conclude that the distinction between vowels and consonants is at least 80% bullshit?