A chemical gas sensor for volatile organic compounds (VOCs) detection at trace level is proposed. In this paper, the development and demonstration of the sensor prototype are presented. The prototype is based on a microcantilever resonator that is fabricated from direct bonding silicon-on-insulator (SOI) wafer. The resonant cantilever employs integrated thermal driving and piezoresistive detecting units, and operates in a self-oscillation system. Polyethylenevinylacetate (PEVA) is deposited on top of the cantilever as gas sensitive layer through a spraying method. The responses of the prototype to relative humidity (RH) and six common VOCs: toluene, benzene, ethanol, acetone, hexane and octane have been tested. The PEVA-coated prototype has trace sensitivity to toluene, benzene, hexane and octane, while is insensitive to humidity. The experimental results provide confirmation that the microcantilever resonator is an excellent platform for chemical gas sensor.