In this paper I surveyed the issues related with phonemes of Korean, particularly focusing on terms and phoneme system. There are various terms representing the plosive, triple correlation bundle, semi-vowel. I reviewed each ones and proposed a more adequate term. In Korean phoneme system, division of alveolar from palatal, classification of ‘h(ㅎ)’, some theoretical problems of diphthong have been issued. I suggested that alveolar and palatal be divided into separate classes, that ‘h’ be classified as a aspirate, that Korean diphthong include the sequence of ‘semi-vowel＋monophthong’ as well as ‘monophthong＋monophthong’, that the interpretion of ‘ㅢ’ and the number of Korean semi-vowel inventory cannot be fixed easily. For the settlement of issues in Korean segmental phonology, it needs to use a phonetic clues efficiently.