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Fast-turnaround, accurate methods for the assessment of threading dislocation (TD) densities in GaN are an essential research tool. Here, we present an in situ surface treatment in which GaN is exposed to a SiH₄ flux at 860°C in the presence of NH₃. Following a 240s exposure to SiH₄, pits associated with screw or mixed-type TD were found to have more than doubled in diameter, as measured by atomic force microscopy (AFM). These pits are associated with step-edge terminations. Additional small pits had appeared, not associated with step-edge terminations, which are believed to relate to edge-type TDs. The total density of pits on the treated surface corresponded to the total dislocation density measured by transmission electron microscopy. Pits related to edge-type TDs are often overlooked in AFM of untreated GaN. As the SiH₄ treatment time is increased, the measured dislocation density initially increases …