With the rapid development of satellite, manned space flight and deep space exploration technology, semiconductor devices are used in extreme environments, especially in radiation and low temperature environment. SiGe HBT is a potential candidate for space applications because of its inherent robustness to total ionizing dose (TID) radiation. However, due primarily to charge collection through the collector-substrate (CS) junction and the relatively low substrate doping., SiGe HBTs are vulnerable to single event effects (SEEs) because of new features of process and structure. Thus, the SEE becomes a key factor in restricting space applications of SiGe HBTs. This paper presents an SEE hardening approach that uses a dummy collector to reduce charge collection in the SiGe HBT. The dummy collector is obtained by using the silicon space between adjacent HBTs. It is obtained without any process modification or area penalty. At first, we build simulation models for both normal and hardened SiGe HBTs, and then carry out SEE simulations respectively. The charge collection mechanism is obtained by analyzing the transient current and charge collection changes at different ion incident positions. Unlike the normal HBT, we can see that charge is continuously collected by the dummy CS junction. This causes more charges diffuse outward and the charges available for collector terminal to be reduced. For all ion incident positions, in the case of hardening, the drift components of charge collection are approximately the same, while the diffusion charge collection components are nearly completely compressed. During SEE, the CS junction either directly collects the deposited charges through drift within the potential funnel or indirectly collects charges after they have arrived at the junction after diffusion. The diffusion length of the carriers is on the order of tens of microns or more. Hence a dummy CS junction should be able to reduce the quantity of diffusive charges collected by the HBT collector. The actual charges collected by the collector are effectively reduced. The emitter and base charge collection also decrease by the dummy collector to different extents. Dummy-collector effectively mitigates the SEE of SiGe HBT. The SEE sensitive area of SiGe HBT is also effectively reduced by half. This work is carried out for the SiGe HBT circuit level radiation hardening design of single event effects