High-voltage nanosecond pulse generators based on series-connected silicon carbide (SiC) mosfets have many prospects in industrial applications. However, the traditional pulse generators cannot achieve voltage sharing and fast pulse rise speed at the same time, which has become one of the key issues limiting the development of generators in some applications. In this article, a novel passive snubber method base on voltage-balancing capacitors is proposed to tackle this issue. First, an analytical model of the pulse rise time of the generator is proposed based on the switching physical principles of the SiC mosfet. Then, a physics-based dynamic voltage-unbalancing model of the series-connected SiC mosfets in the pulse generator is established. Furthermore, based on the established pulse rise model and voltage-unbalancing model of the series-connected SiC mosfets, a voltage-balancing method is proposed which can be used to design optimal voltage-balancing capacitors. Finally, experiments are carried out on a ±5 kV nanosecond-pulse generator. The voltage imbalance ratio of series-connected devices is less than 3.1% and pulse rise time is less than 45.8 ns under different operation conditions, which verify the effectiveness and feasibility of the proposed method.