Ultra hot Jupiters orbit very close to their host star and consequently receive strong irradiation that makes their atmospheric chemistry different from the common gas giants. We study the atmosphere of one of these particular hot planets, MASCARA-2b / KELT- 20b, using four transit observations with high resolution spectroscopy facilities. Three of these observations were performed with HARPS-N and one with CARMENES. At high resolution, the transmission residuals show the effects of Rossiter-McLaughlin (RM) and center- to-limb variations (CLV) from the stellar lines profiles, which we correct to finally extract the transmission spectra of the planet. We clearly observe the absorption features of CaII, FeII, NaI, Hα and Hβ in the atmosphere of MASCARA-2b, and indications of Hγ. The results are consistent with theoretical models of ultra hot Jupiters atmospheres, suggesting the emergence of an ionised gas on the day-side of such planets. Calcium and iron, together with other elements, are expected to be singly ionised at these temperatures and be more numerous than its neutral state.