Thin c-axis films of YBa2Cu3O7-delta have been grown on single crystal (001
) MgO by pulsed laser deposition. The films have been deoxygenated by sinte
ring and annealing in a reduced pressure of O-2. The process is reproducibl
e, controllable and reversible. The reduction in T-c is accompanied by a sy
stematic elongation in c-axis, facilitating an inference of delta. Resistan
ce measurements show a departure from linearity at the pseudogap formation
temperature T*, which has been determined as re function of delta.