Bulk GaN substrates are of significant interest because they offer both high quality and low dislocation densities. Our group has previously reported the formation and movement of dislocations in high quality bulk GaN in response to nano-indentation. We have also proposed a mechanism involving an r-plane (-1012) slip initiated by plastic deformation during a pop-in event, a theory that was supported by molecular dynamics simulations. Herein, we present experimental evidence for this r-plane (-1012) slip mechanism in an indented GaN surface using nano-indentation with an indenter having a smaller radius (∼100 nm) and imparting a lower pop-in load (∼400 μN) compared to the values applied in our previous studies. In addition, this study included TEM observations immediately after the plastic deformation, such that cross-sectional TEM images of the indented surface of the c-plane bulk GaN were acquired just after the pop-in event. The pyramidal dislocation line of an r-plane slip was clearly observed and was inclined by 43° relative to the c-plane surface. Neither a basal c-plane slip nor a prism m-plane slip occurred as a result of dislocation multiplication as secondary or tertiary slip systems, even though these slips had been identified when employing a larger radius indenter and a higher pop-in load. From these experimental results, we were able to confirm that plastic deformation in bulk GaN is initiated via an r-plane slip.