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This Letter presents the design, fabrication and experimental characterisation of a pneumatically actuated positive gain microvalve fabricated using SU-8 and gold over a printed circuit board substrate. The experimental results show that this microvalve has a n-channel metal-oxide semiconductor (NMOS)-like function in fluidic channel networks, with a maximum positive gain of 90 mL/(min bar) and flow regulation of air from 3 to 40 mL/min for a working pressure of 10 mbar. The device has linear and saturation regions as p-channel microfluidic transistors. In addition, a new region named shock zone is obtained experimentally together with the rest, using air both as actuation and control fluid. The new shock zone corresponds to the breakdown region in microelectronic NMOS transistors. The proposed microvalve working as NMOS microfluidic transistor completes the field of transistors regarding the kind of channel. Furthermore, the device can be used as an active device in fluidics circuits and completes both the possibilities of flow control and microfluidic circuits design.