Six-valley effects on electron transient transport in silicon (Si) are investigated by temporal Monte Carlo simulations. The effects on velocity overshoot, carrier repopulation, and average electron energy are studied using two well-known models of Si. Substantial differences in transient carrier repopulation and average energy are found using the two models. For transient carrier velocity, the two models give essentially the same response. A simple one-valley model for Si with optimized parameters is presented for saving computer time when accuracy is not strictly demanded. The significance of these results is discussed.