In this paper, we study the impact of body bias, gate length, and spacer length on various performance parameters of n-type dopingless Silicon on Insulator transistor (DL-SOI). On-off current ratio (I_on/I_off) increases with increase in negative body bias voltage. Simulation study shows that subthreshold swing (SS), drain induced barrier lowering (DIBL) are also improved with negative body bias. A comparative study is also performed between junctionless SOI transistor (JL-SOI) and DL-SOI with respect to body bias voltage. Performance parameters such as SS, DIBL, I_on/I_off are improved in both the devices with negative body bias voltage, but DL-SOI shows higher improvement in I_on/I_off than JL-SOI with negative body bias voltage. DL-SOI also shows lower threshold voltage variation in comparison to JL-SOI device with body bias voltage.