This mixed-methods experimental study aimed at investigating the potential transfer of a social stigma in pronunciation in the L1, to the learning of an L2. In Chilean Spanish, the phoneme /tʃ/ can be realised either as [tʃ] or [ʃ], yet the latter option is socially stigmatised and associated with lower socioeconomic groups. In English, /tʃ/ and /ʃ/ are phonemes, which means that using one over the other is not optional. Such allophonic relationship in Spanish and phonemic relationship in English, together with the social stigma over [ʃ] in Chilean Spanish, provided an ideal scenario to explore this phenomenon. Eighteen high school Chilean speakers were selected for this experiment, where socioeconomic groups and gender were manipulated in Spanish (L1) and English (L2) words with graphemes ch and sh. Through the use of recordings and questionnaires, findings supported previous studies showing a social stigma over the fricative sound [ʃ] in Chilean Spanish. Regarding gender differences, no substantial differences were found among male and female speakers. In relation to a potential transfer of this social stigma to the learning of English, results suggested that there is a tendency to replace the fricative sound /ʃ/ with the affricate sound /tʃ/ in the L2 sh grapheme words, which could be due to the transfer of the social stigma. However, the data gathered from the questionnaires did not support the claim that this phenomenon is indeed happening as a result of transfer of the social stigma. Moreover, an irregular trend across socioeconomic groups was observed. Given these findings, it is speculated that the influence of variables such as teaching methodology or level of English, which were beyond the scope of the study, could explain the results obtained. Regarding the discrepancy found between the recordings and the questionnaires, interviews are suggested in future research to better capture the reasons behind the trend observed in pronunciation.I would like to thank my parents and brothers for supporting me in this academic challenge. I would also like to thank my friends, the one I left in Chile, and the ones that I made in this beautiful country. I would also like to express my sincere gratitude to my supervisor Dr Amanda Cardoso, who was always ready to help and provide insightful feedback throughout this whole dissertation process. Similarly, many thanks to all the incredible MA Linguistics and ELT staff, for all the things I learnt in this intensive year. I am also thankful for the wonderful moments I got to experience with my classmates. Having the opportunity of learning about your culture, lifestyles and traditions is something I will always hold dear in my heart. Many thanks to Catalina Ortiz, Absalón Rojas and Camila Infante, the three EFL teachers who helped me gather the necessary data from their beloved students, in order to conduct this research. Likewise, I would like to acknowledge the Commission for Scientific and Technological Research (CONICYT), which granted me the financial support needed to study this Master’s degree in the University of Leeds. Last but not least, I would like to thank my amazing husband, Cristóbal, for encouraging me to accept this challenge. Thank you for your love, patience, understanding, and for taking care of me when I was completely absorbed in my assignments and dissertation. Thanks for your infinite support in this journey.