By using radio frequency (RF) sputtering, the n–AlInGaN/p–Mg-InxGa1-xN heterojunction diodes were successfully fabricated on Pt/TiO2/Si(100) substrate by using the cermet targets for p–Mg-doped InxGa1-xN (with x = 0, and 0.1) and n–Al-doped InGaN. The target for n–AlInGaN film had an Al content of 7.5% and In content of 15%, while the target for p–InxGa1-xN film had Mg content of 10%. The experimental data indicated that the n–AlInGaN film with a smooth surface and a surface roughness of only 1.54 nm was polycrystalline, had a wurtzite crystal structure, and had electrical properties of carrier concentration of 7.26 × 1016 cm-3 and mobility of 70 cm2·V-1·s-1 at room temperature (RT). By I–V tests at RT, the n–AlInGaN/p–Mg-InxGa1-xN heterojunction diodes displayed a high breakdown voltage beyond 20 V, low leakage current of 8.73 × 10-9 A at -1 V, and a turn-on voltage of ~2.5 V. Testing with a temperature range of 25–150°C, the leakage current of the n–AlInGaN/p–Mg-GaN device at a bias of -5 V increased from 1.69 × 10-7 A at 25°C to 9.88 × 10-6 A at 150°C. The optimum barrier height and ideality factor of the n–AlInGaN/p–Mg-InGaN device were found to be 0.57 eV and 5.6 at 25°C, respectively, while these values investigated at 150°C were 0.67 eV and 4.5. In addition, the electrical characteristics of n–AlInGaN/p–Mg-InxGa1-xN heterodiodes recognized in the thermionic–emission mode at a wide temperature range can be calculated by applying the Cheung and Norde methods.