The invention relates to a device for the reactive conversion of gaseous streams at high temperatures in excess of 1000° C. Said device comprises a reaction chamber (8) with an inlet opening for the gaseous streams to be converted, in particular a burner head (2) and an outlet opening for the converted gaseous streams. In order to guarantee the highest possible conversion performance, the reaction chamber (8) has a narrow construction, extending longitudinally from the inlet opening to the outlet opening to form a controlled gaseous flow, thus preventing a circulatory flow in the reaction chamber (8). To achieve reaction conditions that are as adiabatic as possible, the reaction chamber (8) is thermally insulated with a layer (7) that has a porous foam and/or fiber structure. In the simplest embodiment, the reaction chamber (8) is cylindrical, thus achieving a tubular flow reactor construction for the entire device.