Secondary ion mass spectrometry (SIMS) and Rutherford Backscattering Spectrometry (RBS) techniques were used to determine InxGa1-xN and AlxGa1-xN compositions. While RBS is generally considered a quantitative technique for compositional analysis, SIMS has not been. We have applied a new analytical technique, which reduces the matrix effect in SIMS analysis, to accurately determine stoichiometry. The composition of InxGa1-xN (AlxGa1-xN) in the multiple layers and quantum well of the LED can be measured by SIMS, but is inaccessible to RBS.