To passivate Si-SiO2 dangling bonds, metal–oxide–semiconductor field-effect transistor devices are usually treated with hydrogen. Herein, the effects of such a treatment on the crystallization behavior on N-doped, Ge-rich Ge2Sb2Te5 phase-change materials for memory applications are investigated using synchrotron X-ray diffraction (XRD) in situ during heat treatment. Uniform thin films, and laterally confined, metallized ones (simulating devices of different complexity) of initially amorphous N-doped GGST are investigated. The specimens are heated up to 450–500 °C at a rate of 2 °C/min. Some of the specimens are treated with H/D; the equivalent untreated specimen is investigated for each of them. Crystallization onsets are estimated by quantification of the crystallized quantity during material transformation from the XRD patterns. In thin films, the hydrogen treatment results in lowered crystallization temperatures of the emerging cubic, metastable Ge2Sb2Te5 phase. Its trigonal, thermodynamically stable polymorph always forms, but its crystallization temperature is unchanged. Patterned and metallized samples show less differences, are strongly textured, and no trigonal phase is observed. It is shown that certain questions might only be answered at large-scale facilities where high energy photons are available at high flux, allowing data acquisition during the annealing process with a temperature resolution sufficient for a fine description of the sample transformation.