ZnO microcrystals are synthesized through a facile solution method and characterized by field-emission scanning electron microscopy, transmission electron microscopy, selected area electron diffraction and X-ray diffraction. The ethanol sensing properties of these microcrystals are investigated by spin-coating them on a silicon substrate with Pt electrodes to fabricate a micro-structure sensor. The sensitivity is up to 8 when the sensor is exposed to 50 ppm ethanol, and the response time and recovery time are 10 s and 20 s, respectively. A contact-controlled model is established to explain the sensing properties of the microcrystals, which provides another approach to realize high-performance gas sensors.