The evolution of nanoscale pores or dimples during ion etching of GaN was used to measure the magnitude of the curvature-dependent roughening. GaN(0001) surfaces were ion etched with glancing-incident, 300 eV Ar and nitrogen ions using a beam flux of 3.6× 1014 ions cm-2 s-1. The samples were rotated during the etching, and the sample temperatures maintained between room temperature and 600 °C. This etch process smoothened the surface but left nanoscale dimples or pores with diameters between 30 and 800 nm. The density of these dimples remained constant during the etch process but the dimples were observed to grow larger in size until coalescence occurred. The formation of these ion-induced, nanoscale features was analyzed in terms of a continuum model that included a curvature-dependent roughening term and a smoothening term. The integral of the removed material was measured in order to directly determine the curvature dependence of the sputter yield. From the evolution of the dimple dimensions, we measured the roughening coefficient as 43±5 and 28±4 nm2 s at 460 and 315 °C, respectively, which are four orders of magnitude larger than that calculated using curvature-dependent sputtering alone. Preliminary measurements of the roughening coefficient versus temperature show a minimum at a temperature of about 365 °C.