Glides, /j/ and /w/, are recognized as semivowels in Vietnamese, and they are conventionally and widely written as /i̯/ and /u̯/, respectively (Phạm & Mcleod 2016, Tran, Vallée & Granjon 2019). The implication of the conventional transcription of the two semivowels is that they are non-syllabic /i/ and /u/, suggesting that /i̯/ and /u̯/ might have similar or nearly identical acoustic properties with the two high vowels /i/ and /u/. As the semivowels are only allowed in onsets and codas, and the vowels are allowed in nuclei (Kirby 2011, Phạm & Mcleod 2016, Brunelle 2017, Tran et al. 2019), the only difference between the two semivowels and the two vowels might be where they can appear. That is, the semivowels might be non-syllabic positional variants of the high vowels that appear in onsets and codas (Levi, 2008). To examine this hypothesis, audio files in which a native female speaker of Southern Vietnamese recites the 200 Swadesh words in her dialect were collected, and the first formant (F1) and the second formant (F2) of each word that contains either /i/, /u/, /i̯/ or /u̯/ were measured using Praat (Boersma & Weenink 2020). Analyses on the F1 showed no significant difference on the F1 between /i/ and /i̯/ (p = .97) or /u/ and /u̯/ (p = .78). Similarly, there was no significant difference on the F2 between /i/ and /i̯/ (p = .91) or /u/ and /u̯/ (p = .91). The results support that /i/ and /i̯/ as well as /u/ and /u̯/ have nearly identical phonetic properties.