A method of forming a dielectric layer on a further layer of a semiconductor device is disclosed. The method comprises depositing a dielectric precursor compound and a further precursor compound over the further layer, the dielectric precursor compound comprising a metal ion from the group consisting of Yttrium and the Lanthanide series elements, and the further precursor compound comprising a metal ion from the group consisting of group IV and group V metals; and chemically converting the dielectric precursor compound and the further precursor compound into a dielectric compound and a further compound respectively, the further compound self-assembling during said conversion into a plurality of nanocluster nuclei within the dielectric layer formed from the first dielectric precursor compound. The nanoclusters may be dielectric or metallic in nature. Consequently, a dielectric layer is formed that has excellent charge trapping capabilities.