Ultrathin organic thin‐film transistors (OTFTs) have received extensive attention due to their outstanding advantages, such as extreme flexibility, good conformability, ultralight weight, and compatibility with low‐cost and large‐area solution‐processed techniques. However, compared with the rigid substrates, it still remains a challenge to fabricate high‐performance ultrathin OTFTs. In this study, a high‐performance ultrathin 2,7‐dioctyl1benzothieno3,2‐b1benzothiophene (C8‐BTBT) OTFT array is demonstrated via a simple spin‐coating method, with mobility as high as 11 cm2 V−1 s−1 (average mobility: 7.22 cm2 V−1 s−1), on/off current ratio of over 106, switching current of >1 mA, and a good yield ratio as high as 100%. The ultrathin thickness at ≈380 nm and the ultralight weight at ≈0.89 g m−2 enable the free‐standing OTFTs to imperceptibly adhere onto human skin, and even a damselfly wing without affecting its flying. More importantly, the OTFTs show good electrical characteristics and mechanical stability when conformed onto the curved surfaces and even folded in a book after 100 folding cycles. These results illustrate the broad application potential of this simply fabricated ultrathin OTFT in next‐generation electronics such as foldable displays and wearable devices. A high‐performance ultrathin organic thin‐film transistor (OTFT) array is fabricated via a solution process, with the highest mobility of 11 cm2 V−1 s−1. The thickness of ≈380 nm renders the devices with ultralight weight (≈0.89 g m−2), good conformability, and extreme flexibility. The devices show good electrical characteristics when conformed onto different curved surfaces and even folded in a book.