A novel p-n heterojunction of an alpha-Fe2O3/NiO composite was prepared by precipitation and hydrothermal methods. The structure, morphology and composition of the composite were characterized by numerous spectroscopic methods and its gas sensing properties for triethylamine (TEA) were also tested. The results showed that the composite (Fe/Ni = 4 : 1 atomic ratio) exhibited a fast response approximately 4 times that of alpha-Fe2O3 with excellent selectivity, stability and linear response in the range from 5 to 25 ppm TEA at 140 degrees C, which was due to the large specific surface area of the hierarchical structure and the formation of p-n heterojunctions at the interface of both the metal oxides. Therefore, the composite synthesized in this study is a promising sensing material for the detection of TEA and the work provides a new route to rationally design sensor structures for realizing the synergetic functions of metal oxide semiconductor interfaces.