Method and device for rotating a wafer which is arranged floating in a reactor. The wafer is treated in a reactor of this nature, and it is important for this treatment to be carried out as uniformly as possible. For this purpose, it is proposed to rotate the wafer by allowing the gas flow to emerge perpendicular to the surface of the wafer and then to impart to this gas a component which is tangential with respect to the wafer, thus generating rotation. This tangential component may be generated by the provision of grooves, which may be of spiral or circular design.