Thick, high-purity semi-insulating (SI) homoepitaxial layers on 4H-SiC were demonstrated using a novel compensation scheme controlled by defect-competition epitaxy at C/Si ratios of 1.3 to 1.5. These showed resistivity of ∼109Ωcm. Comparison of secondary ion mass spectra between low-doped epilayers grown at C/Si ratio <1.3 and SI epilayers grown at C/Si ratio >1.3 showed little difference in residual impurity concentrations. A reconciliation of impurity concentration with measured resistivity indicated a compensating trap concentration of ∼1015 cm-3 present only in SI epilayers. High-resolution photoinduced transient spectroscopy (HRPITS) identified them as Si vacancy related centers, with no detectable EH6/7 and Z1/2 levels. Recombination lifetimes of ∼5ns suggest application in fast-switching power devices.High Purity Semi-Insulating 4H-SiC Epitaxial Layers by Defect-Competition Epitaxy: Controlling Si Vacancies. M.V.S.Chandrashekhar, I.Chowdhury, P.Kaminski, R.Kozlowski, P.B.Klein, T.Sudarshan: Applied Physics Express, 2012, 5[2], 025502