In this letter, total ionizing dose (TID) response of bulk n-type Fin Field-Effect Transistor (n-FinFET) is investigated with the various number of fins. Experiments show that only the single fin n-FinFET exhibits significant radiation damage, while the degradation of multi-fin devices is observed to be minimal. 3D TCAD simulations indicate that relative positions between fins and STI play a critical role in the TID response of n-FinFET.