We have fabricated diodes with different sized Si quantum dots (QDs) by precisely controlled low-pressure chemical vapor deposition using a pure SiH₄ gas and studied the effect of dot size on field electron emission properties of their multiple-stacked structures. At an applied bias of ~9 V, the emission current of ~4.0 nm height dot-stacks is two orders of magnitude higher than that of ~5.9 nm height dot-stacks. These results can be interpreted in terms of an increase in the number of electrons with higher kinetic energy due to the increase in discrete energy levels associated with the reduction in the dot size, which suppresses electron scattering within the dot, and the decrease in curvature of the dot might be enhanced the electric field concentration.