The quality of silicon wafers used as substrates for microelectronic devices is measured in terms of the type, size and density of defects formed during crystal growth process. The native point defects such as vacancies and self-interstitials diffuse, react and aggregate to form intrinsic defects in the silicon wafers. We investigated the point defect behaviour using the kinetic lattice Monte Carlo (KLMC) model. The KLMC method has been applied extensively in various forms to the study of microdefects in silicon wafers. The purpose of this paper is to demonstrate the phenomena of void defect formation. The size and density of void defects are usually affected by system temperature, vacancy-vacancy reaction and vacancy-impurity reaction. In this paper, we study the temperature effect and the vacancy concentration effect. The simulation results with various temperatures are well matched with our experimental data, and the relationship between temperature and vacancy density describes well the phenomena of void defect formation. This is the first time such KLMC simulation results have been reported.