Abstract: A microfluidic system and method, suitable for “lab-on-a-chip” applications, by which a bubble is inflated in fluid flowing through a microfluidic channel at a predetermined location along the channel and the bubble is maintained at that location to stop flow through the channel in the manner of a valve. The microfluidic channel is formed on a semiconductor chip and a pair of electrodes is formed one on each side of the channel, whereby a bubble is electrochemically inflated between the electrodes and held in fixed position by the channel wall when a voltage is applied across the fluid incident to connecting the electrodes to a voltage source. When the voltage is removed, deflation of the bubble valve rapidly occurs to restore flow. The present invention provides flow control in a microfluidic system regardless of channel cross-sectional geometry and with no moving parts and low power consumption. Moreover, the present invention may be practiced using existing fabrication techniques.