This paper reports remarkably reliable MEMS relays having a unique two-step spring system and a heat sink insulator. The two-step spring system is designed to reduce Joule-heating by lowering contact resistance. The heat sink insulator is proposed for efficiently removing heat generated in the contact area. These two features are firstly adopted in the MEMS relay for minimizing thermal damage in high current level, thus enhancing reliability significantly. The fabricated relay demonstrated contact resistance of 2 mΩ, which is the lowest value compared to the state-of-the-art . In addition, the relay was operated up to 5.3x106 cycles at 1 V/200 mA in an air and hot switching condition with negligible contact resistance variation. The resulting lifetime is 500 times longer than that of the commercial MEMS relay measured in the same test setup.