AlN bulk crystals of different crystallographic orientations were etched in aqueous KOH solution (general etchant) and molten KOH/NaOH eutectic alloy (defect selective etchant). In the general etchant, the aluminum polar surface (0001) was found to be stable while the nitrogen polar (0001) surface and non-polar m-plane (1010) surfaces showed significant etching. Etch patterns on nitrogen polar surfaces consisted of complete coverage of hexagonal pyramids while the m-plane surfaces were etched in a layer-by-layer mode. TEM studies revealed that the observed etch hillocks on nitrogen polar surfaces were not associated with extended structural defects. When etched in a defect-selective etchant, the aluminum polar surface showed well-defined hexagonal etch pits, with an etch pit density (EPD) of 2×104 cm−2. The nitrogen polar surfaces and m-plane surfaces showed etch features similar to the one obtained during general etching, however, the etch feature density was significantly lower. The etch mechanisms, etch kinetics, as well as the correlation between the observed etch features and structural defects in bulk crystals will be discussed.