Abstract The study compares how L1 Chinese and Japanese speakers perceive L2 English semivowels (/j/ and /w/) preceding high vowels (/i/ and /u/). In Chinese, [j] and [w] serve as phonetic variants of /i/ and /u/, respectively. However, /j/ and /w/ are distinct phonemes in Japanese, although Japanese /w/ lacks the roundness feature found in English /w/. Participants completed experiments with a discrimination task and an identification task. While the discrimination task revealed no differences in /j/ and /w/ perception between the groups, the identification task showed that the Japanese speakers outperformed the Chinese speakers in their perception of /j/, suggesting an L1 “phonemic over phonetic” advantage. However, the Japanese speakers did not outperform the Chinese speakers in their perception of /w/, suggesting that an L2 feature unexploited in the L1 (i.e., roundness) can impede perception. These findings underscore the importance of considering both phonemic status and features in L2 speech perception.