10.1039/C4CE01339E ; LEDs with enhanced light extraction efficiency and sensors with improved sensitivity have been developed using porous semiconductors. Here, the growth of porous GaN epitaxial layers oriented along the [0001] crystallographic direction on Al2O3, SiC, AlN and GaN substrates is demonstrated. A lattice mismatch between the substrate and the porous GaN layer directly affects the structure and porosity of the porous GaN layer on each substrate. Deposition of unintentionally doped n-type porous GaN on non-porous p-type GaN layers allows for the fabrication of high quality rectifying p¿n junctions, with potential applications in high brightness unencapsulated GaN-based light emitting diodes and high surface area wide band gap sensor devices.