Piezoresistive effect (PRE) has been utilised as a dominant sensing principle in a wide range of applications. Since its discovery, piezoresistive effect has attracted considerable interest in developing sensors with higher sensitivity. However, a giant piezoresistive effect in intrinsic semiconductors with reliability is still facing great challenges such as the limited nature of piezoresistive materials and dynamic trapping of charge carriers at surfaces of nanostructures under mechanical strain. Therefore, finding a new strategy and approach to enhance the PRE not only improves the performance of piezoresistive sensors but also can open a new research direction. This research aims to discover and demonstrate the opto-electronically enhanced piezoresistive effect, which significantly improves the performance of the PRE. This research also analyses the key parameters contributing to this tuneable giant piezoresistive effect. In addition, a demonstration of the unprecedented enhancement of sensitivity, tunability, stability, and the expansion of detectable range in a pressure sensor by applying the opto-electronically enhanced piezoresistive effect is investigated. A new technology for harvesting light energy to selfpower and simultaneously sense mechanical acceleration in a monolithic structure, which is an expansion of application of the opto-electronically enhanced piezoresistive effect, are developed in this research. Finally, the feasibility of integrating light source into the sensors instead of using an external light source for the opto-electronically enhanced piezoresistive effect is demonstrated. The discovery of the opto-electronically enhanced piezoresistive effect and its demonstrated applications can pave the way for development of ultrasensitive sensor technology and a new technology for harvesting light energy and self-powering NEMS/MEMS sensors. The outstanding results of this research have been demonstrated by papers reviewed and published in high quality journals such as Nature Communications (IF=11.878), Journal of Materials Chemistry C (IF=7.059), and Nano Energy (IF=15.548). A part of these results is featured on the back cover of Journal of Materials Chemistry C. In addition, parts of the results from this research are under review second time at Materials Horizons (IF=13.870) and have been submitted to Small (IF=11.459).