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We report microfabrication of a millimeter-scale fuel cell with onboard fuel and a passive control mechanism. This unique power source has a total volume of 9 muL (3times3times1 mm3), which makes it the smallest fully integrated fuel cell reported in the literature. The first generation of this device delivered an energy density of 254 Wmiddoth/L. The device uses a reaction between a metal hydride, LiAlH4, and water vapor to generate hydrogen in a reactor. The generated hydrogen exits the reactor through a nanoporous silicon wall to reach a hybrid silicon/Nafion membrane electrode assembly. A passive micro- fluidic control system regulates hydrogen generation through controlled delivery of water vapor to the metal hydride based on the reactor pressure. The development of this unique power source greatly benefits the portable electronics industry and enables future technologies that require significantly high energy density power sources such as cognitive arthropods ("thinking" insect- sized robots). This paper provides details of the device micro- fabrication processes, component integration, and performance analysis. [2008-0168].