Semi Vowels (W,Y) are also called as Semi Consonants

The Word Alphabet is taken from first two Greek alphabet, i.e Alpha & Beta. There are 26 English Alphabets, out of which 21 are consonants and 5 are vowels, but 2 letters i,e W & Y are semi vowels. Semi Vowels are also called as Semi Consonants. These letters sound like vowels in the word "Cow,Boy, Toy etc. whereas, they sound like consonants in the word "Yet, Wet".