Abstract: The invention relates to a method and to a device for the thermal treatment of substrates, in particular semiconductor wafers, and to a holding unit for substrates. In the method, in a process unit having a process chamber and having a plurality of radiation sources, one or more substrates are held in a box having a lower part and having a cover, wherein the lower part and the cover form a holding space for the substrate therebetween. Furthermore, the following steps are performed in the method: loading the box and the substrate into the process chamber and closing the process chamber; purging the holding space of the box with a purging gas and/or a process gas before the box and the substrate contained therein are heated to a desired process temperature in order to establish a desired atmosphere inside the box; and heating the box and the substrate contained therein to the desired process temperature by means of thermal radiation emitted by the radiation sources.