This paper reveals a critical limitation in the electro-hydraulic analogy between a microfluidic membrane-valve (lMV) and an electronic transistor. Unlike typical transistors that have similar on and off threshold voltages, in hydraulic lMVs, the threshold pressures for opening and closing are significantly different and can change, even for the same lMVs depending on overall circuit design and operation conditions. We explain, in particular, how the negative values of the closing threshold pressures significantly constrain operation of even simple hydraulic lMV circuits such as autonomously switching two-valve microfluidic oscillators. These understandings have significant implications in designing self-regulated microfluidic devices. Electric circuit analogy is widely used in microfluidic circuit design and analysis. For example, electric resistors correspond to microfluidic channel resistances and capacitors to flexible membranes. The analogy is based on the similarity in equations between these circuit components. Since the theory and simulation methods of electric circuits are wellestablished, they greatly facilitate the design and analysis of various microfluidic circuits. 1 Recently, analogy has been drawn between electronic transistors and microfluidic membrane-valves (lMV), which are used for self-regulated microfluidic circuits such as frequency-specific flow regulators, 2 digital logic circuits, [3][4][5][6] and oscillators. [7][8][9] Like an electronic circuit that operates itself with only a power source and thus minimize the use of its external controllers, the self-regulated microfluidic circuits have the potential to greatly reduce reliance on expensive and complex external controllers, which are barriers to broader use of microfluidic devices. A lMV is a crucial component that enables operation of self-regulated microfluidic devices through its on-off switching.Similar to the electronic transistor, the lMV's on-off switching is determined by the relative difference between the source (P S ) minus gate pressure (P G ) versus the threshold pressure ( Figure 1). As depicted in Figure 1(a), when P S is sufficiently greater than P G , the membrane of the lMV deflects down and the lMV is on (open). In other words, the lMV is on when P S À P G is greater than opening threshold pressure (P th-open ). To turn off (close) the lMV, P S À P G is less than closing threshold pressure (P th-close ). In typical silicon transistors, 10,11 the difference between on and off threshold voltage is negligible, thus providing a large parameter space for the design and operation of large-scale integrated circuits. Pneumatic lMVs also exhibit small differences between opening (P th-open ) and closing (P th-close ) threshold pressures. 5,12 However, in self-regulated microfluidic devices, the detailed characteristic of lMV's threshold pressure in the context of other microfluidic parameters such as fluidic resistor and inflow rate is largely unknown.Here, we report that P th-open and P th-close are significantly differe...