In this thesis, we apply mild hydrostatic pressure on device-scale organic and hybrid semiconductor samples. We focus on organic and inorganic hybrid perovskites and small organic molecular crystals and perform steady-state and time-resolved optical measurements to study the absorption, emission and charge carrier/exciton dynamics in these material systems. We demonstrate the power of hydrostatic pressure for studying the structure-property relationship of organic and hybrid semiconductors. Even mild pressure can significantly change the properties of an organic/hybrid material. The results of this thesis provide insights into design of novel organic/hybrid semiconductors, and suggests potential approaches of improving the performance of (flexible) devices by building-in strain, for example by epitaxial growth of active layers.