The recent trends in healthcare ICT technologies promise high quality of care, whereas the variety and diversity of healthcare data increase the challenges of information exchange. With healthcare systems facing poor communication and information exchange difficulties, interoperability has become the holy grail of Health IT. While several techniques and researches are conducted to face this challenge, a global solution is still missing, as only particular scenarios are being currently addressed. This paper emphasizes on achieving semantic interoperability across multiple electronic health records (EHRs), through ontologies and Model-driven Engineering techniques. A multi-stepped approach is proposed that transforms EHR datasets into syntactic models and metamodels, in order to be finally transformed into their semantic structure through a mechanism that translates them into a common ontological representation