The influence of number fluctuation and position variation on channel dopants and gate metal grains on tunneling field-effect transistors (TFETs) have been discussed in comparison with metal-oxide-semiconductor FETs (MOSFETs). Based on the simulation results of randomly generated device samples, the shape of the statistical threshold voltage (V(th)) distribution of TFETs associated with individual variation sources such as random dopant fluctuation (RDF) and work-function variation (WFV) have been found to be significantly different than that of MOSFETs. This analysis provides a detailed insight into the variation sources related to underlying physics of TFETs.