Thin epitaxial films of monoclinic pure and cubic yttria‐stabilized (YSZ) ZrO2were deposited onto Si(100) by electron‐beam evaporation. The degree of crystalline perfection was controlled by the growth temperature. Epitaxial YBa2Cu3O7−xfilms were grown on these buffer layers by KrF excimer laser ablation. Optimum crystalline and electrical quality, characterized by a transition temperatureTc0of 86–89 K, a critical current densityjcof 106A/cm2at 77 K, and a channeling minimum yield of 12% was obtained on YSZ buffers showing a minimum yield of 7%. Even a 14‐nm‐thick YSZ buffer enabled the growth of an YBa2Cu3O7−xfilm withTc0of 86 K and a minimum yield of 12%. With decreasing quality of the YSZ buffer layers the crystalline quality of the superconductor also decreased. The disorder in the YBa2Cu3O7−xfilms, however, increased more slowly than in the buffer layers, so that even on an amorphous buffer the YBa2Cu3O7−xexhibited a pronounced texture with a minimum yield of 72%. The comparatively rough surface of the monoclinic pure ZrO2severely hampered thec‐axis alignment of the YBa2Cu3O7−x, resulting in superconductor films of inferior quality.