In the field of extrusion, a very promising high performance extruder was introduced to the European plastics industry in 1999. This new type of single-screw extruder combines a grooved plasticizing barrel with a barrier screw. Compared to conventional extrusion systems, these extruders have by far a higher output and product quality among other advantages such as lower processing costs and lower energy consumption. In the past, both Newtonian and non-Newtonian models were developed to calculate and predict the melting rate along the flow channel. The aim of this paper is to present experimental investigations on the processes within the melting zone of a single-screw extruder with a grooved plasticizing barrel. To visualize the melting mechanisms, screw extraction experiments as well as dynamic pressure measurements were performed. By means of screw extraction experiments a solid bed was clearly identified only in the solid channel and a melt pool only in the melt channel. Analysis of the dynamic pressure signals also showed the same behavior and therefore allowed in-line characterization of the melting process. Thus, theoretical concepts about the melting mechanisms could be confirmed experimentally.