YBa2Cu3O7-x/MgO/YBa2Cu3O7-x trilayers fabricated by an excimer laser ablation technique were studied by transmission electron microscopy. MgO/YBa2Cu3O7-x bilayers, as-deposited and treated, were also studied. Sandwiched MgO was formed to be islands during the top-layer YBa2Cu3O7-x deposition.