InAlN/GaN　heterostructure　field-effect　transistors　(HFETs)　have　been　grown　and　fabricated　on　Fe-doped　semi-insulating　c-plane　GaN　substrates.　The　problematic　parasitic　leakage　caused　by　interface　charge　between　the　epitaxial　layers　and　the　GaN　substrate　as　well　as　any　adverse　effect　of　the　substrate　surface　damage　caused　by　the　mechanical　chemical　polish　employed　on　the　substrates　has　been　circumvented　by　using　a　combination　of　inductively　coupled　plasma　dry　etching　and　in　situ　H-2　etching.　As　a　result,　the　current　leakage　for　100　mu　m　separation　mesa-to-mesa　was　reduced　down　to　3x10(-9)　A/mm　at　10　V　voltage　bias　for　a　320　mu　m　mesa　pad　width　normal　to　the　current　flow　direction　and　the　corresponding　GaN　buffer　resistivity　was　about　3.5x10(8)　Omega　cm.　Owing　to　the　good　thermal　conductivity　of　GaN　substrates,　the　HFETs　exhibit　much　less　current　degradation,　compared　to　those　on　a　sapphire　substrate,　at　high　drain　biases.　Likewise,　the　dc　and　pulsed　I-V　characteristics　were　reasonably　similar,　suggestive　of　negligible　drain　current　lag.　A　dc　saturation　drain　current　density　of　1.0　A/mm　was　achieved　at　zero　gate　bias.　For　HFETs　with　1.1　mu　m　gate　length　and　90　mu　m　gate　width,　the　maximum　extrinsic　dc　transconductance　was　275　mS/mm.　(C)　2010　American　Vacuum　Society.　[DOI:　10.1116/1.3481138]