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The Global Positioning System (GPS) is the primary means of Positioning, Navigation, and Timing (PNT) for most civilian and military systems and applications. The rapid growth in autonomous systems has created a widespread interest in self-contained Inertial Navigation System (INS) for precise navigation and guidance in the absence of GPS. The microscale PNT systems need both specialized and low cost fabrication technologies to cost effectively bring these technologies to market. We describe an ultra-clean (low leak rate) wafer-level vacuum encapsulation microfabrication process of Micro-Electro-Mechanical Systems (MEMS) based sensors and devices. Using this process we have fabricated inertial sensors, frequency reference resonators, and pressure sensors. In addition to providing excellent resistance to shock and vibration, this combined microfabrication and packaging method would allow the use of high volume low cost plastic packaging at the device level. The microfabrication process is an 8” wafer process based on high aspect ratio bulk micromachining of a 30 μm thick single-crystal silicon device layer that is vacuum encapsulated at 10 mTorr between two silicon wafers with the demonstrated leak rate of only 6.5 × 10−18 atm cm3/s.