This study demonstrates all-optical Raman scattering study of dislocations in ammonothermally grown alpha-GaN crystal and identifies an edge (a)over-right-arrow-type threading dislocation (TD) using a confocal Raman 3-D imaging technique. These findings make possible the characterization of volumetric stress field and low TD density distributions over a large area on bulk alpha-GaN single crystal. The dislocation type effects on Raman shift are also discussed in detail (in order to identify the edge (a)over-right-arrow-type and mixed (a)over-right-arrow + (c)over-right-arrow-type TDs, and theorize the invisibility of the screw (c)over-right-arrow-type TDs). Authors are not aware of any previous reports using the confocal Raman 3-D imaging to identify the edge (a)over-right-arrow-type and mixed (a)over-right-arrow + (c)over-right-arrow-type TDs.