In this study, the effects of chemical treatment on the properties of MOS capacitors and metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) were studied. The structure consist of Al2O3/u-GaN/AlN buffer/ Si substrate and Al2O3 (10 nm)/u-AlGaN (25 nm)/u-GaN (2μm)/AlN buffer/Si substrate for MOS capacitor and MOS-HEMT device, respectively. There are four chemical treatment recipes, which consist of organic solvents, oxygen plasma, BCl3 plasma, dilute acidic solvent, hydrofluoric acid and RCA-like clean process to remove the metal ions, organic contamination and native oxide. Four different chemical treatment recipes treated the surface of u-GaN before Al2O3 was grown on the treated surface to reduce the interface state trap densities (Dit). The Dit value was calculated from measurement of C-V curve with 1M Hz frequency. The formation of interface state trap of u-GaN surface is modified by different chemical solution of varied chemical treatment recipe, which further influence the breakdown voltage (Vbk), on-resistance (Ron), threshold voltage (Vth) and drain current (Id) of MOS-HEMT. The Vth of MOS-HEMT with organic solvents clean treatment is -11.00V. The MOS-HEMT after BCl3 plasma and organic solvents clean treatment shows the lowest Vth of -9.55V. The electronic characteristics of MOS HEMT device with four different chemical treatment recipes were investigated in this article.