We investigated the effect of the deposition rate on the surface morphology of Si nanowhiskers (NW) deposited by e-beam evaporation using the vapor-liquid-solid growth mechanism. The roles of deposition rate and corresponding surface diffusion on the Si NW growth kinetics were examined. Two growth regimes were observed within the investigated range of deposition rates. Films belonging to these two regimes were found to have characteristically different formations and surface morphologies. We found that the length-diameter curves of NWs switch from decreasing to increasing at a certain critical evaporation rate. The surface morphology is composed of long whiskers (~1 μm) tapered with faceted sidewalls in the high deposition rate regimes (above 1.2 Å/s) due to their length which is comparable with the adatom diffusion and the direct adsorption of Si atoms on the sidewalls. The characteristic morphology was composed of shorter straight whiskers in the low deposition rate regimes (0.6–1 Å/s) because of the higher contribution of Si adatoms diffusing from the substrate to the NW growth.