Effective, permanent tuning of the whispering gallery modes (WGMs) of p-i-n doped GaN microdisk cavity with embedded InGaN quantum dots over one free spectral range is successfully demonstrated by irradiating the microdisks with a ultraviolet laser (380nm) in DI water. For incident laser powers between 150 and 960 nW, the tuning rate varies linearly. Etching of the top surface of the cavity is proposed as the driving force for the observed shift in WGMs, and is supported by experiments. The tuning for GaN/InGaN microdisk cavities is an important step for deterministically realizing novel nanophotonic devices for studying cavity quantum electrodynamics.In recent years, there has been tremendous progress in the understanding of lightmatter interactions (cavity quantum electrodynamics, or cQED) in semiconductor systems [1][2][3][4][5][6][7][8] . Strong coupling has been observed for GaAs-based cavities coupled to embedded InGaAs quantum dots 2, 3, 4 , and studies have also extended to other semiconductor materials 5 . Such studies provide a promising route to the realization of quantum information technology 6-9 and ultra-efficient light emitting devices 10, 11 . In particular, InGaN quantum dots (QDs), well coupled to GaN-based optical cavities offer the potential of highly efficient devices operating at room temperature in the