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GaN-based LEDs with different thickness of n-GaN have been grown on 4-in. Si(1 1 1) substrate by metal–organic chemical vapor deposition. Quality of GaN epilayer has been evaluated by X-ray diffraction (XRD). Strain information in the structure has been directly investigated by means of micro-Raman scattering. It can be concluded that the compressive strain has varied to a tensile one with increasing n-GaN thickness from 0.5 to 2.0 μm. As a result, in a sample with a 2 μm n-GaN thickness, the tensile stress of GaN epilayer was calculated to be 0.44 GPa. Moreover, the strain states of GaN epilayer have been revealed from the variations of its a - and c -lattice constants, which have been calculated using XRD results. In addition, emission peak shift of GaN epilayer has been confirmed by cathodoluminescence measurement, and light output power of LEDs has also been measured. Nevertheless, some correlations in this study would inspire researcher to design much more reasonable GaN-LEDs structures in future. [ABSTRACT FROM AUTHOR]