When an initial /s/ precedes a voiceless stop in English, the aspiration is lost, and the voice onset time (VOT) is significantly shortened. This causes an allophonic variation of English stops based on context. This paper intends to comparatively investigate this phenomenon in English, Kurdish and Kurdish EFL learners from two proficiency levels. (40) participants which are divided among four groups (Kurdish, English, learners G1 and learners G2) are asked to read lists of words including voiceless stops preceded by /s/, constructed in English and Kurdish. Each stop in the list has two examples followed by a high and a low vowel. All the participants are asked to repeat each word three times to provide three tokens. These productions are recorded and VOT values are acoustically measured. Results are then statistically analyzed to check the significance of variable interactions. Results have shown that Kurdish voiceless stops preceded by /s/ are more aspirated than those of English in similar contexts and thus produced with longer VOT values. This indicates that Kurdish learners need to modify their voiceless stop production when speaking English. Results also show that advanced Kurdish learners have improved at pronouncing the aspirated English stop variety, but they still produce it with a noticeably extended VOT.