This dissertation presents research performed in two broad areas of Micro Electro Mechanical Systems (MEMS): transient vaporizable electronics and chip-scale gas sensors. Transient polymer-based vaporizable electronics and MEMS for controlled disappearing of microsystems are presented in the first half of the dissertation. Components for gas sensing with ion-mobility spectrometry are presented in the second half. For vaporizable polymer-based electronics, the key MEMS component is a graphene-on-silicon nitride single-shot valve presented here. The valve is triggered thermo-mechanically with 142 mW input power in 15 milliseconds using 2:2 mJ of energy - a 100 reduction from previous reports in literature. It is used for exposing highly reactive pristine alkali metals such as rubidium and cesium to ambient oxygen for exothermic vaporization of the polymer substrate. An architecture for integrating the alkali metals with sodium biflouride (NaHF2) etch sources for etching electronics on oxide substrates is also presented. In addition to demonstrating a transient system, the graphene-on-nitride membrane is also used as a thermo-gravimetry platform for multi-mode characterization of picograms of polymer. The atomically thin graphene sheet serves as a resistive heater for ramping temperature on the nitride membrane. During this, the resistance variation of the graphene is used for electrical characterization of the polymer-graphene surface interactions. The polymer vaporization as a result of temperature ramping on the nitride is sensed mechanically as a resonance frequency shift of the membrane. Finally, a novel architecture for producing controlled transience of silicon-based electronics is presented. Polypropylene carbonate (PPC) is used as a connective layer to hold a silicon substrate intact. PPC can be vaporized to selectively remove parts of the substrate, on demand, using localized integrated thin-film heaters. The key component of the ion-mobility based gas sensors is the multielectrode ion-detector array developed in this thesis. Laser-micromachining is used for direct maskless patterning of silicon wafers, to define the detector array topology. The sensor uses a lateral electric field to separate gases on different electrode-islands of the array, based on their ion-mobility and a transimpedance amplifier is used to sense the current generated due to the ions. High-aspect ratio channels are realized using vertical stacking of patterned silicon structures, which are used for obtaining distinct signatures of different gas mixtures for pattern-based recognition. To produce flow of ions of the gas to be analyzed, a thin-film piezoelectric bimorph cantilever of length 1000 m is fabricated and used as an ion-pump. The micro-fabricated lead zirconate titanate (PZT) on silicon dioxide beams are able to produce flow rates up to 186 L=min min and flow velocity as high as 7 cm=sec. A sense cantilever of length 800 m is cofabricated with the drive pump to sense lateral air-motion and provide feedback for turbulent air-flow in the device. To produce the ion species from the neutral gas molecules for detection with the IMS array, a pyroelectric lithium niobate (LiNbO3) ionizer is developed. The ionizer uses an integrated resistive heater for producing an average ion current of 9:36 pA during the stochastic ionization process and peak ion current as high as 44:8 nA. All system components operate at < 5V, for compatibility with low-voltage CMOS platform requirements. This is crucial for integration in portable electronics such as laptops and cell-phones the target for these sensors.