This book presents an electrostatically actuated, normally open, low pressure-drop silicon membrane microvalve. It is intended to be used in an ion mobility spectrometer in order to enhance its operating range. The fabricated microvalve shows expected characteristics except hysteresis behavior and its quality of repeatability, which are discussed in the book reasoning them by parasitic charges in the silicon dioxide and built-in oxide voltage. Pull-in and relaxation characteristics of the diaphragm are also discussed extensively. Nitrogen flow rate is 30.05 sccm at 50 mbar pressure drop. Experiments show 0.0139 sccm leakage rate for an initial flow of 5 sccm which corresponds to a characteristic ratio of 359.7 using 200 V. This can be improved to 1798.6 using 300 V. This work is also an example to microsystem and microvalve design, guiding the reader from design to characterization following each step, and providing details such as governing equations, simulation codes in ANSYS, lithography masks, and fabrication steps. Thus, it will hopefully be beneficial for beginners in MEMS with its simple language as well as for intermediate level designers seeking detailed information.