Capacitance-gate voltage [C(V)] characteristics of inversion layer of the cylindrical silicon nanowire (SiNW) MOS are simulated using a two-dimensional Schrödinger-Poisson (SP) self-consistent solver with explicit cylindrical coordinates and quantum-mechanical treatment within the effective mass approximation. Our simulation results demonstrate strong effects of confinement of electron wavefunctions on spatial and spectral characteristics of excess (inversion) electrons in SiNW-based MOS device, which eventually yield in significant oscillations in C(V) dependencies, simulated at temperatures below 40 K and SiNW radii below 8 nm.