In this paper, a heterojunction FinFET on heterodielectric BOX is proposed and this device is named as heterojunction heterodielctric BOX (HJHDB) FinFET, to eliminate the effect of trap density. The interface trap charge is considered at the interface of Si-HfO$_2$ in technology computer aided design (TCAD) simulator. The effect of trap charges on transfer characteristics, surface potential, subthreshold swing (SS) and threshold voltage are investigated for both HJHDB FinFET and conventional FinFET (C-FinFET) taking box height as a parameter. Such analysis is also demonstrated by varying the temperature in wide ranges for both the devices. It is seen that there is no effect of fixed trap in HJHDB FinFET even at high temperature, whereas a noticeable amount of trap effect isobserved for C-FinFET. Furthermore, the effect of trap level on various electrical parameters is presented for both devices and an insignificant amount of trap level variation is observed for HJHDB FinFET. On the other hand, a visible impact of trap level is observed in C-FinFET.