The invention relates to a method and a device for generating hydrogen (5), wherein an input (1) comprising carbon is fed longitudinally through a tube-shaped reaction chamber (Z), together with water steam (2), and is thereby converted by steam reforming, and hydrogen (4) formed during steam reforming is continuously drawn off out of the reaction chamber (Z) through a separating wall (T), said wall being selectively hydrogen-permeable at least in segments, and at a pressure less than the pressure in the reaction chamber (Z) and greater than the ambient pressure, having greater purity than product (5), characterized in that a separating wall (T) is used, the selectively hydrogen-permeability segments thereof being disposed such that a hydrogen partial pressure drop exists over the entire surface of each of such segments between the reaction chamber side and the hydrogen extraction side (W).