In this work, the growth mechanism of epitaxial YSZ on Si with native oxide by PLD was investigated. The possibility to control different sources of oxygen in the PLD process was exploited to control the chemistry during the scavenging of oxygen from the native oxide by YSZ. In conditions corresponding to optimum YSZ crystalline quality, silicide formation was prevented due to partial oxidation of the YSZ plasma and sufficient flux of oxygen from the ambient to the growing film. In this regime, significant regrowth of silicon oxide occurred, catalyzed by the deposited YSZ film. Thickness increase of the silicon oxide before growth had to be prevented by starting the depostion as soon as possible after reaching growth temperature. These findings show that the contributions of all sources of oxygen can and should be controlled in order to obtain reproducible YSZ growth.