In this paper we present a “polymer-last” approach for the fabrication of (partly) flexible and stretchable sensors assemblies. The “Flex-to-Rigid” (F2R) platform is based on this approach and especially designed for the fabrication of very small sensor systems which can be folded into, or around the tip of minimal invasive instruments such as laparoscopic instruments, catheters or guide-wires. As an example the fabrication and assembly of a combined pressure and flow sensor on the tip of a 360 μm diameter guide-wire is presented. The F2R platform uses standard silicon manufacturing equipment in a standard production environment and is therefore suitable for high volume production. Using the same “polymerlast” approach stretchable circuits have been fabricated. As an example a stretchable Micro-Electrode Array for electrophysiology is demonstrated. The paper ends with an outlook on an entire new field in micro fabrication where living cells are co-integrated with silicon bases micro-systems resulting in truly Living Chips.