Dependence of the depletion length in semiconductor quantum dot of spherical form on its radius is studied by means of solution of the Poisson equation in "depletion layer approximation". It is shown that spherical form of the interface increases the depletion length (in comparison with the case of planar interface) substantially stronger than the cylindrical form does. Critical value of the quantum dot radius at which depletion encompasses all volume of the structure (full depletion) is equal to root 3W(p) in contrast to root 2W(p) for the case of quantum wire (W-p is the depletion length for planar interface). (C) 2015 Elsevier Ltd. All rights reserved.