To process aggregate queries in massive database application efficiently, semantic cache technology is extended in this paper, which is mostly used in small scale database applications at present. Firstly, a formal semantic cache model for aggregate queries is proposed. Based on this model, a semantic cache system called StarCache is built. The key technologies of StarCache about aggregate query processing, cache replacement and consistency maintenance etc. are also discussed in this paper. StarCache has been integrated in StarTP, which is a parallel database middleware developed by a team of the National University of Defense Technology, and has been applied to a large national project.