Atom Probe Tomography (APT) is a technique that couples time of flight mass spectroscopy with an approximate point projection imaging. The advent of ultra-short duration pulsed-lasers with high optical quality has made rapid acquisition of data from materials with poor electrical conductivity practicable. APT analysis of the III-nitrides based devices has value due to the technological significance of these materials. 3D metrology of the active regions of III-nitride based devices provides insight into their electrical/optical performance. APT analysis of a commercial grade c-plane light emitting diode showed that the indium fluctuations in the active region significantly impacted the device's internal quantum efficiency, droop behavior, and current-voltage curves. Comparative analysis was performed on 20-21 and 20-2-1 Gallium Nitride (GaN)-based semipolar light emitting diodes (emission wavelength ~450 nm) using APT. The quantification of 3D Indium distribution in the single quantum well active region in these devices revealed a higher Indium incorporation in the 20-2-1 GaN light emitting diode single quantum well, consistent with the predicted polarization influenced potential energy landscape in the well. APT analysis of aluminum indium nitride nanostructure grown on Gallium Nitride demonstrated the influence of substrate orientation and growth methodology on nanoscale morphology. Gallium Nitride nanorods were also characterized to analyze the indium incorporation in the Indium gallium nitride quantum wells grown on the nanorods' sidewalls.