Atomic-scale nanofacets were observed in semipolar and InGaN quantum wells (QWs)/GaN quantum barriers interfaces. Transmission electron microscopy studies showed that these nanofacets were mainly composed of , and planes, which led to significant fluctuations in QW thickness. Atom probe tomography studies were carried out to visualize the nanofacet structure. The In composition in the InxGa1−xN alloys followed a binominal distribution despite the formation of the nanofacet structure. One-dimensional (1D) Schrödinger-Poisson drift-diffusion simulation showed that these nanofacets and associated QW thickness fluctuations will lead to a large wavelength shift and a broadened spectral linewidth for semipolar QWs.