Structural and electrical properties of YBa2−xSrxCu3Oyprepared under ambient oxygen pressure were systematically investigated for 0≤x≤2.0. Samples with high Sr contents,x≥1.7, showed semiconductive properties with an activation energy of ∼150 meV at high temperature,T≥80 K. At low temperatures,T≤80 K, activation energy dropped to ∼3.00 and ∼0.85 meV forx=1.7–1.8 andx=1.9–2.0, respectively. It is argued that YSr2Cu3Oyis likely to have a tetragonal structure and that the disorder introduced by Sr substitution affects electrical conduction, which involves charge hopping between the CuO chains at high Sr contents. ©1996 American Institute of Physics.