In the present study we demonstrate the ability of changing the electronic properties of a semiconductor surface by adsorbing polyelectrolytes. For this purpose polyethylenimine (PEI) polymers were adsorbed onto the van der Waals surface of the layered structure semiconductor WSe2. For comparison the surface properties of the as grown and chemically treated surface were investigated by standard and photoassisted tunneling spectroscopy. In the case of the chemically treated sample a strong change in the I/V characteristics could be observed.