The　AlGaN/GaN/InGaN/GaN　double　heterojunction　high　electron　mobility　transistors　(DH-HEMTs)　sample　has　been　grown　by　MOCVD　on　(0　0　0　1)　sapphire　substrate.　The　structure　features　a　7　nm　In0.046Ga0.954N　interlayer　determined　by　Rutherford　backscattering　(RBS).　Since　the　polarization　field　in　the　InGaN　interlayer　is　opposite　to　it　in　the　AlGaN　layer,　an　additional　potential　barrier　is　introduced　between　the　two-dimensional　electron　gas　(2DEG)　channel　and　buffer,　leading　to　enhanced　carrier　confinement　and　improved　buffer　isolation.　The　GaN　layers　between　the　AlGaN　layer　and　InGaN　interlayer　are　divided　into　two　layers　consisting　of　GaN　channel　layer　which　provides　high　mobility　2DEG　grown　at　1070　degrees　C　and　GaN　spacer　layer　grown　at　the　same　temperature　as　InGaN　interlayer　(800　degrees　C)　to　prevent　indium　diffusion.　RBS　measurement　confirms　that　the　3　nm　GaN　spacer　layer　isolates　the　InGaN　interlayer　well　and　free　from　diffusion.　Hall　measurement　has　been　performed,　the　mobility　as　high　as　1552　cm(2)/V　s　at　room　temperature　is　obtained　and　the　sheet　carrier　density　is　1.55　x　10(13)　cm(-2).　The　average　sheet　resistance　is　331　Omega/sq,　respectively.　The　mobility　obtained　in　this　paper　is　about　20%　higher　than　similar　structures　reported.