On the basis of the continuity of subthreshold current at the interface of trapped charges in the channel between fresh and damaged regions, a new interface quasi-Fermi potential (IQFP) model for the nanosheet FET with interface-trapped charges (ITCs) is developed. With the IQFP, the subthreshold current degraded by the ITCs for both N-FET and P-FET can be completely developed. We found that the IQFP can be strongly affected by both the distribution and polarity of the ITCs. Owing to the distribution of positive/negative ITCs near the drain side for N-FET/P-FET, the decreased threshold voltage will cause noise margin (NM) degradation. In contrast, the threshold voltage will be increased by the distribution of negative/positive ITCs near the source side for N-FET/P-FET, which resists the degradation of the NM. The NM caused by the balanced transistor strength between P-FET and N-FET can be monitored using the IQFP. This model can also be extended to other multi-channel-potential FETs comprising the subthreshold logic gate.