In order to investigate the factors affecting the bonding of third-generation semiconductor materials SiC and III-V compounds InP, different pretreatment steps are implemented on SiC and InP wafer substrates to explore the methods to realize the successful bonding of SiC/InP and to improve its bonding strength. In the wide application of wafer bonding technology, plasma plays an indispensable role by reducing the process temperature. Although many studies on plasma-assisted direct wafer bonding have been reported, in-depth studies on the plasma itself are still insufficient. The existing literature mainly focuses on the optimization of the parameters of plasma surface treatment, while the studies on the surface cleaning steps before and after plasma activation and the annealing process, which need to be comprehensively investigated to maximize the bond strength, are still incomplete. In particular, ultrasonic cleaning as a pretreatment step and its application before plasma activation on the bonding effect deserve in-depth study. In this study, we evaluate the various process steps of SiC/InP wafer bonding through specific experimental studies. The focus is on the effect of ultrasonic cleaning on bond strength, while the parameters of plasma surface treatment and low-temperature annealing conditions are optimized. The experimental results show that ultrasonic cleaning is a key part of its bonding success, and that the selection of the appropriate plasma gas, the adjustment of the instrumental power, and the processing time all have an impact on the bonding effect of the final wafer pair.