Plasma Electrolytic Oxidation (PEO) is a versatile surface engineering process able to deliver industrial and consumer needs such as in automotive, aerospace, biomedical, and electronics applications. Processing parameters in fabricating thin and dense PEO coatings are a challenge. Understanding the effects of electrolyte composition and treatment time on coating morphology and characteristics is crucial to enhance and widen the applications of PEO coatings on aluminium. In this study, prolonged PEO treatment tends to produce thicker, more porous, rougher surfaces and increases alpha alumina phase within the inner region of the PEO coating. For insulated metal substrate applications, the need to minimize surface defects such as porosity and contact resistance are essential. Nanoparticles of alpha alumina additives in the electrolyte assist in lowering surface roughness and porosity up to 54% in the coatings as well as increasing alpha alumina phase at the near surface region. Silicate anions tend to produce thicker, rougher and porous PEO coatings. However, silicate species are necessary for nanoparticle and microparticle deposition during the PEO process. Whilst phosphate anions are required in stabilizing AlN microparticles against hydrolysis. Therefore, phosphate and silicate are needed for AlN deposition in PEO. Electrophysical properties of oxide ceramics were investigated to gain an understanding of fundamental properties such as charge carrier concentration and dielectric strength of coatings produced from PEO. PEO on Al with nanoparticles of alpha alumina additives produced n-type semiconductor films with dielectric strength 59-76 V per micronmeter.