Intersubband transitions in self-assembled quantum dots are studied by using a multiband tight-binding method. A picture different from that by the single-band effective-mass approximation is presented to reveal the origin of the polarization of the intersubband transitions. It is shown that the symmetry of those minor components from the valence bands in the electronic states accounts for the polarization of the intersubband transitions. A microscopic theory is presented to explain the pattern of symmetry of these minor components in the electronic states. The result is compared with a recent experiment. © 2008 American Institute of Physics.