The structure of Ba2YCu3O6 has been determined by neutron diffraction powder profile analysis. The cell is tetragonal P4/mmm with a=3.8570(1) A ̊ and c=11.8194(3) A ̊. The cations are in a perovskite type arrangement, with Ba and Y ordered on the A site to give a cell tripled along c. The oxygens occupy only 2 3 of the perovskite anion sites and are ordered such that 1 3 of the Cu is two-fold coordinated and 2 3 is five-fold coordinated. This configuration can be derived from that of the superconductor Ba2YCu3O7 by removing the oxygen atoms along the b axis at the ( 0,1 2,0) position. A pressed pellet exhibited semiconductivity with a band gap of 0.21eV from 125-300K. The compound is described as Ba2YCu1+Cu2+2O6.