Within the framework of the vapor-liquid-solid process of Si nanowire growth, an expression describing the Si nanowire growth rate is derived and fitted to multiple experimental data sets with excellent agreement. The derivation is based on the two-dimensional island nucleation-growth process which appeared to have been first mentioned by Givargizov and Chernov [Sov. Phys. Crystallog. 18, 89 (1973)]. This nucleation-growth process is in principle different from the conventional diffusion limited or reaction barrier limited processes. © 2013 AIP Publishing LLC.