In this work we present for the first time correlation of lateral uniaxial tensile strain and I–V characteristics of GAA Si NW n-MOSFET, all measured on the same device. Micro-Raman spectroscopy is employed for direct strain measurement on devices to exploit the main sources of process-induced strain, found to be accumulation of mechanical potential energy in the Si NWs during local oxidation and releasing it in the form of local lateral uniaxial tensile stress in the Si NW by out-of-plane mechanical buckling as well as lateral in-plane elongation during stripping the hard mask and the grown oxide. A triangular GAA Si NW with 0.6 GPa peak of lateral uniaxial tensile stress, fabricated using this bulk top-down technology, exhibits promising improvements e.g. of the normalized drain current (ID/Weff) up to 38%, of the transconductance (gm/Weff) up to 50%, of the low field mobility by 53% with a peak of 64% in the peak stress region, compared to a reference device. The mobility extraction originally takes into account the measured strain profile in the channel.