In this study a gas detection microfluidic system with a gas integrated pumping by thermal creep was realized. First, microfluidic and thermal simulations were done to determine the microsystem dimensions. Heat distribution in all microsystem was then simulated using Comsol Multiphysics software. These results allowed us the best material choices suited for our application. The microsystem includes an integrated gas sensor in a microchannel, with heater and trioxide tungsten (WO 3) sensitive layer. Conventional microelectronic methods have been used to achieve this microsystem. The thermal stability and the temperature gradient within the microsystem have been studied. Finally, the first microsystem tests under ammonia with concentrations between 10 and 100 ppm at 473 K have been made and give reproducible conductivity variations.