This study aims to examine the phonological interference of the Madurese language on the English pronunciation of students at Islamic Boarding School Raudlatul Ulum 2. The research uses a descriptive qualitative approach focusing on identifying forms of phonological interference that appear in students' speaking skills, both in segmental and suprasegmental aspects. Data were obtained through audio recordings of students' speaking practice, classroom observations, and brief interviews. A total of 1,071 phonetic transcriptions were analyzed using the International Phonetic Alphabet (IPA). The results showed 441 pronunciation errors, or 41.18%. The most dominant type of error was sound substitution (18.49%), followed by addition (11.77%), omission (6.72%), and combination (4.20%). Additionally, suprasegmental disturbances were found in the form of incorrect word stress placement, flat intonation, and unnatural speech rhythm. These findings indicate that the phonological system of the Madurese language exerts a strong influence on students' English pronunciation. Therefore, phonological interference becomes a major challenge in teaching English speaking within the Islamic boarding school environment
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