Dataset and analysis code accompanying the manuscript "Fractional AC Josephson effect in a topological insulator proximitized by a self-formed superconductor," available at https://arxiv.org/abs/2110.01039. This dataset includes measurements of Josephson junction devices with (BiSb)2Te3 weak links, whose Pd-Te superconducting leads are self-formed through deposition of Pd on the (BiSb)2Te3. In junctions with the prefix "Al", an Al layer is added to the superconducting leads following Pd deposition. The dataset includes transport measurements of Shapiro steps under radiofrequency excitation as well as DC electronic transport measurements. Analysis code is provided in the accompanying iPython notebooks.