Direct conversion of single-layer SnO nanoparticles to multi-layer SnO2 nanoparticles is achieved by annealing in an O-2 ambient at 700 degrees C. For 50 ppm ethanol, the sensitivities of the multi-layer SnO2 nanoplates are more than double that of single layer SnO2 nanoparticles, which are also formed from the single-layer SnO. The higher sensitivity of the multi-layer nanoplates is attributed to their larger surface/volume ratio. The facile fabrication of interconnected multi-layer SnO2 nanoplates at low temperature directly on a Si substrate and sensing chip without the aid of catalysts offer vast advantages over competing methods for the fabrication of high-sensitivity SnO2 sensors.