Abstract Microchannels prepared in poly(dimethylsiloxane) (PDMS) structures were coated with a liquid emulsion which was then crosslinked creating a porous layer on walls of the channels. The emulsion contained a PDMS prepolymer mixed with a porogen. In this initial work water was used as a porogen. Having pumped the emulsion through the microchannel, the whole structure was cured at 120 °C in order to crosslink the emulsion and allow to evaporate a porogen. As a result a porous layer on the microchannel's walls was obtained with a so-called open porosity. The evaluation of the porosity was done with the help of numerical analysis. Pores with an equivalent diameter on the order of 4–6 μm were fabricated. Further, fabrication of gas sensor containing a porous layer with a pH indicator is described.