Abstract and figures Surface Acoustic Wave (SAW) sensors demonstrate superior sensitivity in detection of chemical agents. Due to their solid state design and fabrication compatible with modern technologies, SAW chemical sensors are extremely reliable. The sensor is modeled as a two-port device with parts represented by equivalent circuits. Change of output frequency as a function of vapor concentration is calculated. The oscillator circuit with SAW sensor in the feedback loop is designed. The SAW sensor is used for modifying the oscillator frequency. The presence of chemical vapor is then detected by monitoring this frequency shift.