We have computed a theoretical library of stellar spectra, from Near-UV to Near-IR, with varying abundance ratios of alpha, C, N, Na, among others. The current project is aimed at building-up a new set of semi-empirical stellar spectral libraries that incorporate there abundance variations. This is performed by adapting the theoretical library to the instrumental set-up of a newly observed library based on the X-Shooter instrument at the Very Large Telescope, which is called XSL. The adapted theoretical library is used to derive abundance-dependent spectral responses. The differential spectral responses to the varying abundances are applied to the real stars to create semi-empirical versions of the XSL library with varying abundance values of mainly alpha-elements and carbon. The new semi-empirical XSL libraries will incorporate reliable differential corrections for cool stars, which are particularly relevant in the NIR range of galaxy spectra. The XSL is particularly advantageous as it has moderately high resolving power of 10000 with a wide spectral range coverage from the U to the K band (i.e. from ~0.3 to 2.3 micron) but also with an unprecedented coverage of atmospheric parameters. Such advantages make it ideal to compute stellar population models to interpret a rather wide variety of galaxy spectra.