A detailed presentation of the latest version of the Leti-UTSOI compact model is provided. Leti-UTSOI2 is the first available model able to describe the behavior of low-doped ultrathin body and buried oxide fully depleted silicon-oninsulator transistors in all bias configurations, including strong forward back bias. In this part, a full analytical calculation of interface potentials, valid for all regimes of independent doublegate device operation, is detailed. This analytical computation, which is the heart of Leti-UTSOI2, provides explicit expressions for all quantities required to build dc and ac core models.Index Terms-Analytical models, compact modeling, fully depleted silicon-on-insulator (FDSOI), independent double-gate, semiconductor device modeling, SPICE, ultrathin body and buried oxide (BOX), ultrathin body BOX (UTBB).