Flexible electronics based on rigid conventional crystalline semiconductors such as silicon and compound semiconductors is emerging as a new class of technology. At present, the existing approaches for realizing flexible electronics from those materials have focused on maintaining the performance of the original device. Here, we demonstrate a new approach for tailoring the electronic and optoelectronic properties of high-performance flexible devices through strain engineering. In this work, we use flexible gallium arsenide (GaAs) devices as a model system. We show that layer transfer through substrate cracking with a pre-tensioned nickel film can be utilized for engineering the electronic band structure of flexible GaAs devices. We empirically and theoretically quantify the effect of the 'engineered' residual strain on the electronic band structure in these flexible GaAs devices. Photoluminescence (PL) and quantum efficiency (QE) measurements indicate the widening of the GaAs energy bandgap due to the residual compressive strain. More importantly, our strain engineering method is universal and can be readily extended to other flexible material systems such as gallium nitride.