Formation of highly-uniform and densely-packed arrays of GaAs dots by selective epitaxy using diethylgallium-chloride and arsine is reported. The arrays of GaAs dots are imaged using atomic force microscopy (AFM). Accounting for the AFM tip radius of curvature, the smallest GaAs dots formed are 15-20 nm in base diameter and 8-10 nm in height with slow-growth crystal planes limiting individual dot growth. Completely selective GaAs growth within dielectric-mask openings at these small size-scales is also demonstrated. The uniformity of the dots within each array ranged from 6% for the larger dots to 16% for the smallest dots (normalized standard deviations of the areas of individual dots within each array).