The isolation of single-atom-thick layer of graphite, very well known now as graphene, done by A.Geim and K.Novoselov (Nobel prize in physics 2010) in 2004 was a truly revolutionary breakthrough which opened up a new field of research and had a pronounced impact on multiple domains ranging from solid state physics and surface chemistry up to cosmology. The outstanding properties of this material triggered a surge of interest for 2D materials and shortly after the discovery of graphene a plethora of other 2D materials rapidly flourished. This thesis focuses on 2D van-der-Waals semiconductors and their heterostructures. Here we present a detailed experimental study on electronic and optical properties of these materials and demonstrate their high technological relevance as indispensable components for future electronic devices.