Hydrogen sulfide (H2S) plays an important role as an intercellular and intracellular signaling molecule, yet its targets are not well understood. As a molecule it easily evaporates and it is hard to acquire stable concentration for in vitro studies, constituting a major problem for the field to identify its downstream targets and function. Here we develop a microfluidic system that can provide consistent and controllable H2S levels in contrast to the current method of delivering large bolus doses to cells. The system relies on the permeability of H2S gas through a polydimethylsiloxane thin membrane. A hydrogen sulfide donor, sodium hydrosulfide, is perfused in the microchannels below the gas permeable membrane and gaseous H2S diffuses across the membrane, providing a stable concentration for up to 5 hours. Using electrochemical sensors within 3 ppm range, we found that H2S concentration was dependent on two parameters, the concentration of H2S donor, sodium hydrosulfide and the flow rate of the solution in the microchannels. Additionally, different H2S concentration profiles can be obtained by alternating the flow rate, providing an easy means to control the H2S concentration. Our approach constitutes a unique method for H2S delivery for in vitro and ex vivo studies and is ideally suited to identify novel biological processes and cellular mechanisms regulated by H2S.