peer reviewed ; Similar to neighbouring German varieties, the recent language history of Luxembourgish is subject to an ongoing merger of the alveolopalatal fricative [ɕ] (deriving from the palatal fricative [ç]) and the postalveolar fricative [ʃ], leading progressively to the collapse, for example, of the minimal pair frech [fʀæɕ] 'cheeky, impertinent' and Fräsch [fʀæʃ] 'frog'. The present study will draw on a large dataset— which has been recorded using an innovative smartphone application—consisting of fricative realisations of more than 1,300 speakers. In an acoustic analysis, various parameters of the two fricatives will be studied (Centre of Gravity, spectral moments, Euclidian distance, DCT coefficients) and correlated with the speaker’s age. The results show that the merger is acoustically manifest for nearly all age groups. Only the oldest speakers keep the two fricatives distinct.