In this paper, the effects of device orientation, geometry, and strain (uniaxial and biaxial) on the electrostatic properties of different silicon gate-all-around metal-oxide-semiconductor field-effect transistors are thoroughly investigated. We show how the electron density changes with the device orientation and how it depends on the geometry, size, and strain. Although the threshold voltage is weakly dependent on the orientation, we show that it is strongly affected by the geometry, strain, and size. In addition, the suitability of the isotropic effective mass model is investigated for cylindrical devices. We prove that this model is not able to mimic electron density obtained with a nonisotropic model. However, if an appropriate isotropic effective mass value is selected, the behavior of the threshold voltage can be reproduced.