This study investigates a novel approach of fast thermal desorption on a micro-sorbent trap for analyzing ambient volatile organic compounds (VOCs) by gas chromatography with flame ionization detection. Unlike conventional approaches, the temperature feedback mechanism for temperature control was abandoned, which often poses a limit to the heating speed due to slow response of the sensor and the control algorithm. Instead, a series of programmed a.c. pulses was given to the Ni-Cr wire coiled around the micro-trap to perform instant heating from room temperature to 250°C within a fraction of a second, maintained at 250°C during injection, and subsequently to 300°C for trap cleaning. Temperature fluctuation around a high temperature set point could be maintained within ±10°C. Significant improvement in resolution and peak height was obtained compared to a trap with temperature feedback and control algorithm. While keeping resolution at a satisfactory level, the sub-second desorption approach allows faster chromatography and at the same time increases the sensitivity of VOC analysis.