With the development of new technologies, researchers have recently focused their interest on flexible electronics to improve the interaction between users and devices. In this context, integrated ultra-low-pressure sensors remain a technological challenge. Here, we show that organic single crystal-based air-gap transistors fabricated by soft lithography are extremely sensitive to mechanical strain and pressure. When low forces are applied to the suspended semiconducting crystal (rubrene), the gated transistors show that drain currents as output signals are extremely sensitive to the deformations. Incredibly high gauge factors, over 4000, are measured using this technique. Further investigation shows that the contact resistance at the rubrene-gold interface is responsible for the high sensing performances. Such a platform is also able to detect sound waves with high sensitivity, making these simple devices suitable for applications in pressure sensing.