This study presents a mechanical design approach to fabricate high-quality semiconductor fibres with ultralong, fracture-free, and perturbation-free properties. The method involves understanding and controlling stress development and capillary instability during three stages of fibre formation: viscous flow, core crystallization, and subsequent cooling. By optimizing these stages, the researchers achieved continuous, high-quality semiconductor fibres with well-defined interfaces between semiconductor cores and metal electrodes, enabling optoelectronic fibres and large-scale optoelectronic fabrics. The study highlights the importance of selecting appropriate cladding materials, such as aluminosilicate glass (ASG), to minimize stress and prevent cracking in semiconductor cores. The optoelectronic fibres demonstrated excellent performance, comparable to commercial planar-type photodetectors, with high sensitivity, low noise, and robust mechanical properties. These fibres can be woven into functional fabrics and have potential applications in healthcare, robotics, wearable communications, and assistive technology. The research provides fundamental insights into extreme mechanics and fluid dynamics, addressing the growing demand for flexible and wearable optoelectronics. The study also demonstrates the fabrication of optoelectronic fibres with single-core and dual-core structures, capable of sensing and transmitting light, and their integration into wearable devices for real-time monitoring and communication. The results show that the optoelectronic fibres can withstand mechanical stress, including bending, torsion, and compression, making them suitable for underwater and other harsh environments. The study emphasizes the importance of mechanical design in achieving high-performance semiconductor fibres and opens new possibilities for the development of advanced fibre-based optoelectronic devices.This study presents a mechanical design approach to fabricate high-quality semiconductor fibres with ultralong, fracture-free, and perturbation-free properties. The method involves understanding and controlling stress development and capillary instability during three stages of fibre formation: viscous flow, core crystallization, and subsequent cooling. By optimizing these stages, the researchers achieved continuous, high-quality semiconductor fibres with well-defined interfaces between semiconductor cores and metal electrodes, enabling optoelectronic fibres and large-scale optoelectronic fabrics. The study highlights the importance of selecting appropriate cladding materials, such as aluminosilicate glass (ASG), to minimize stress and prevent cracking in semiconductor cores. The optoelectronic fibres demonstrated excellent performance, comparable to commercial planar-type photodetectors, with high sensitivity, low noise, and robust mechanical properties. These fibres can be woven into functional fabrics and have potential applications in healthcare, robotics, wearable communications, and assistive technology. The research provides fundamental insights into extreme mechanics and fluid dynamics, addressing the growing demand for flexible and wearable optoelectronics. The study also demonstrates the fabrication of optoelectronic fibres with single-core and dual-core structures, capable of sensing and transmitting light, and their integration into wearable devices for real-time monitoring and communication. The results show that the optoelectronic fibres can withstand mechanical stress, including bending, torsion, and compression, making them suitable for underwater and other harsh environments. The study emphasizes the importance of mechanical design in achieving high-performance semiconductor fibres and opens new possibilities for the development of advanced fibre-based optoelectronic devices.