Abstract A compact analytical model is presented for device electrostatics of nanoscale Cylindrical Gate (CylG) Gate-All-Around (GAA) MOSFET, using isomorphic polynomial function for potential distribution. The model is based on solutions of 3D Laplace and Poisson’s equations for subthreshold and strong inversion region respectively. In this paper, the short-channel effects are precisely accounted for by introducing z dependent characteristic length and the developed electrostatics is tested against analysis of crossover point for device under test. Further, the modeled subthreshold slope for lightly doped CylG GAA MOSFET has been improved by introducing z dependent characteristic length and the position of minimum center potential in the channel is obtained by virtual cathode position. A new model is proposed for threshold voltage, based on shifting of inversion charge from center line to silicon insulator interface.