Etching wide bandgap semiconductors including SiC and GaN, has been challenging. Achieving damage-free device quality high aspect ratio nanostructures is even more difficult. Currently, to produce SiC or high aspect ratio structures, ICP-RIE is generally used, which often results in high energy ion induced damages.Metal-assisted chemical etching (MacEtch) defies the isotropic nature of chemical etch by utilizing a patterned metal catalyst for spatially defined etching of semiconductors. MacEtch has been successfully demonstrated for various types of semiconductors, including Si, GaAs, InGaAs, AlGaAs, InP, InGaP, GaN, b-Ga2O3, SiC. The metal catalyst type that has been proven to be effective include Au, Pt, Ir, Ru, TiN, CNTs, and graphene. Aspect ratios produced using MacEtch can readily exceed 100:1 in some cases, while limited in other cases. The resulted tapering and porosity are strong function of the etch kinetics for the particular semiconductor material, metal catalyst type and pattern, and etchant condition. The loading effect is determined by the local carrier generation rate and mass transport rate. Depending on how the etching evolves relative to the catalyst pattern and additional assistance, we classify MacEtch into forward, inverse (i-MacEtch), magnetic-fielded guided (h-MacEtch), self-anchored-catalyst (SAC-MacEtch), vapor phase (VP-MacEtch), and UV assisted (UV-MacEtch).In this work, we report the successful demonstration of SiC and GaN nanostructures with various sidewall morphologies using UV-assisted i-MacEtch. Produced structures are characterized as a function of etch conditions by SEM, 3D profilometer, AFM, reflection and Raman spectroscopy, as well as the interface properties using Schottky barrier diodes and MOSCAP structures. This work lays the foundation for producing 3D wide bandgap device structures with damage-free pristine surfaces and interfaces, as well as controlled defect engineering for quantum states.