Due to the introduction of N Bottom Assist Layer (NBAL), the superjunction structure of relatively small aspect ratio could be used in 4HSiC semisuperjunction vertical doublediffused metal oxide semiconductor field effect transistor (VDMOSFET), so that the cost and difficulty of manufacturing process could be reduced. In this paper, a twodimensional simulation structure of the device is established based on the device simulator Atlas. The single event burnout (SEB) effect of 4HSiC semi-super-junction VDMOSFET and 4H-SiC superjunction VDMOSFET are comparatively studied, then the influence of NBAL doping concentration on the antiSEB ability of 4H-SiC semi-super-junction VDMOSFET is studied. The results show that, under condition of the same drain voltage, the peak value of the electric field in the N- drift/N+ substrate junction of semisuperjunction VDMOSFET is 27％ lower than the counterpart of the superjunction VDMOSFET owing to the NBAL. The SEB threshold voltage (VSEB) of superjunction VDMOSFET is 920 V, while the counterpart of semi-super-junction VDMOSFET is 1 010 V, so that the anti-SEB capability of semi-super-junction VDMOSFET increases by 10％ when compared with super-junction VDMOSFET. With the gradual increasing of NBALdoping concentration, the anti-SEB ability of VDMOSFET is firstly enhanced and then weakened, i. e., there is an optimal doping concentration of NBAL to make the ability of the anti-SEB the strongest.