By applying medium frequency (MF) powered twin magnetron arrangements, typical problems of reactive direct current (DC) sputter deposition of electrically insulating materials can be solved. Inherent properties of this new deposition method are a high ion bombardment of the substrate during deposition and the possibility to deposit transparent layers in the transition mode of the cathode characteristic. This leads to modified film properties compared to the DC method. This is shown here for the case of SnO2.