The study of phase decomposition and crystallization of amorphous alloys by small‐angle x‐ray scattering requiresinsitumeasurements during heating to avoid statistical errors due to variation in sample thickness and irradiated volume. The early stages of structural changes and phase transformations are best followed by dynamic measurements using high‐intensity x‐rays as obtained from synchrotron radiation. In this paper we present a new heating apparatus designed and constructed for dynamic small‐angle x‐ray scattering measurements on amorphous alloys during heating. Measurements are conducted on wide ribbons of amorphous alloys self‐heated by joule heating. The arrangement is particularly appropriate for such measurements due to the very high electrical resistivity of such amorphous tapes.