Medium- and high-k dielectric films were grown directly on Si by ultraviolet-assisted pulsed laser deposition (UVPLD). It has been found that at the interface between the dielectric and Si, SiO2 layers of various thickness were always formed. The source for this interfacial layer formation could be the physisorbed oxygen trapped inside the growing dielectric layer during the ablation process. When trying to reduce the thickness of this low-k SiO2 layer, a marked decrease in the electrical properties was noticed. The dielectric constant of 50 nm thick barium strontium titanate (BST) thin films deposited at 600 degreesC was around 180 while the leakage current density was below 1 x 10(-5) A/cm(2) at +1.0 V.