Abstract A microelectronic integrated circuit, referred to as the interdigitated gate electrode field-effect transistor (IGEFET), has been coupled with a chemically active electron-beam evaporated copper phthalocyanine (CuPc) thin film to realize a novel gas-sensitive microsensor. The sensor has been utilized to selectively detect parts-per-billion concentration levels of nitrogen dioxide (NO 2) and diisopropyl methylphosphonate (DIMP). The sensor is excited with a voltage pulse, and the time- and frequency-domain responses are measured. The envelopes associated with the normalized difference Fourier transform magnitude frequency spectra reveal features which unambiguously distinguish the NO 2 and DIMP challenge gas responses. The area beneath each response envelope can correspondingly be interpreted as the sensor's sensitivity for a specific challenge gas concentration.