An explicit analytical model for long-channel double-gate junctionless transistors is presented in each operation mode: 1) full depletion; 2) partial depletion; and 3) accumulation. The proposed model calculates potentials, electric fields, mobile charges, and drain current without any implicit function or special functions. The results obtained with the proposed model agree well with the results obtained with a 2-D technology computer-aided design simulation in all modes of operation and for various device structures. Furthermore, a physical insight is provided into reducing variability using the threshold voltage model.