Low temperature (250–300 C) Cu-Cu thermocompression bonding for hermetic sealing application is investigated in this work. Cavities are etched to a volume of 1.4× 10− 3 cm 3 on one group of wafers in accordance with the MIL-STD-883E standard prescribed for microelectronics packaging. The wafer pairs (non-functional cavity wafer and cap wafer) are bonded at 250 and 300 C, respectively, under a bonding force of 5500N for a duration of 1 hr. The bonding medium consists of Cu (300 nm) bonding layer and Ti (50 nm) barrier layer. The cavities are encapsulated by different seal ring size and different seal ring structure. Helium over-pressure in a bombing chamber and helium leak rate detection by a mass spectrometer are used for hermeticity measurement. The measurement results show that the cavities encapsulated at 250 and 300 C exhibit sufficient hermeticity for sealing application. Double-ring structure is found to outperform single-ring structure. Excellent helium leak rates which are smaller than 5.0× 10− 9 atm. cm 3/sec are detected on all the samples. These values are at least 10 times smaller than the reject limit defined by the MIL-STD-883E standard.