The development of native-like memory traces for foreign phonemes can be measured by using the Mismatch Negativity (MMN), a component of the auditory event-related potential. Previous studies have shown that the MMN is sensitive to changes in neural organization depending on language experience. Here we measured the MMN response in 5-6 year-old monolingual German and bilingual Turkish-German kindergarten children growing up in Germany. MMN was investigated to a German vowel contrast and to a vowel contrast that exists in Turkish and in German. The results show that compared to a German control group, the MMN response is less robust in Turkish-German children to the German vowel contrast. The response to the contrast that exists in both languages does not differ between groups. Overall, the results suggest that the Turkish-German children have not yet fully acquired the German phonetic inventory despite living in Germany since birth and being immersed in a German-speaking environment. (Contains 2 tables and 1 figure.)