The surface of platinum thin-film electrodes, which are used for electrochemical biosensors, was investigated by cyclic voltammetry and laser secondary neutral mass spectroscopy (LSNMS). The platinum electrodes act as transducers and amperometrically detect H2O2, which is produced by enzyme reactions, for application as glucose and lactate sensors. The electrode surface and its impurities, which are caused by technological processing steps, have a strong influence on the electrochemical performance of these biosensors. Therefore some of the platinum electrodes were protected by a titanium layer, which was etched away after the final technological processing step to reduce impurities. Alternatively, an oxygen plasma treatment of the platinum electrodes was tested. The influences of the different processing methods on the platinum surface were investigated.