The optical properties of gold semi-shell nanopartilces with different shell thicknesses, physical parameters and inter-particle separations are theoretically studied by discrete dipole approximation method. The numerical results show that the extinction resonance wavelength of semi-shell nanopartiele is first blue-shifted and then red-shifted as the shell thickness increases, the shell thickness corresponding to resonance wavelength shifting to opposite direction increases with the increase of the dielectric constants of inner core material and embedding medium and with that of the inter-part...