AbstractWith the rise of optical computing, phase‐change materials (PCM) are attractive candidates for implementing programmable optical functionalities in photonic circuits. Integrating them as tunable media in photonic waveguides appears to be a simple but effective way to program their optical transfer function in both amplitude and phase through near‐field interactions. This is exactly what is being addressed in this work by integrating Ge2Sb2Te5 (GST) patches on top of silicon waveguides. A scalable fabrication process is described, and the optical properties and programming capabilities are reported obtained from heterodyne interferometry to access the complex transmission of waveguides on the fly. It is reported that both amorphization and crystallization energy thresholds are at least an order of magnitude lower than previous reports, and programming endurance is successfully tested up to 108 cycles, exceeding all previous results obtained with GST or any other PCM for use in photonics. Finally, the morphological and chemical characterization of PCM against aging is presented, revealing a failure mechanism due to phase segregation and ope ning new avenues to further optimize device endurance. As such, these results will be valuable to the large community of scientists seeking to integrate phase‐change materials into advanced photonic architectures where reconfigurability is required.