Abstract Double‐sided metal‐oxide‐semiconductor field‐effect‐transistor processing is demonstrated for the first time on an ultrathin crystalline silicon substrate of 6‐20 μm in a 100 mm diameter wafer format without a carrier wafer, the thinnest free‐standing silicon wafers ever fabricated. The compatibility of the flexible material with conventional semiconductor processing tools is enabled by supporting an interior ultrathin silicon with a surrounding thicker ring of silicon. Current‐voltage characteristics of transistors on ultrathin silicon show performance as expected from bulk silicon, with electron mobility ~1500 cm2 V−1 second−1. Mechanical measurements quantify the handleability.
