High-temperature and high-voltage characteristics of Cu/diamond Schottky diodes were investigated. Cu Schottky diodes showed clear rectification up to ~700°C. The current–voltage characteristics of the diodes at 400°C were almost unchanged after keeping them for 30h, implying they have high stability at ~400°C. The diodes showed specific on-resistance and breakdown voltage of 83.4mΩcm2 and 713V at 400°C, respectively, which are comparable to reported highest values for diamond Schottky diodes and close to the theoretical limit for 6H-SiC at several hundred °C. These results indicate that Cu/diamond Schottky diodes are promising for high-temperature power applications. •High-temperature and high-voltage characteristics of Cu/diamond Schottky diodes were investigated.•Cu/diamond Schottky diodes showed clear rectification up to ~700°C and have high stability at ~400°C.•The diodes showed specific on-resistance and breakdown voltage of 83.4mΩcm2 and 713V at 400°C.