We report measurements of the electrical resistivity at high temperatures for constant oxygen content, or for fixed temperature and varying oxygen content. We show that the Y1Ba2Cu3O6+ compound changes from a metallic to a semiconducting behavior for 0.5. In the semiconducting regime, the characteristic activation energy is oxygen dependent and reaches 0.37 eV for =0.25. In the metallic regime, the conductivity is approximately linear in the oxygen content while on the semiconducting side, excess conductivity arises from thermally activated processes. © 1988 The American Physical Society.