A method and apparatus for gasifying organic materials in a gasification reactor and vitrifying residual ash in a melting furnace comprising introducing a charge containing organic materials into said reactor, heating the charge sufficiently to thermally decompose and gasify the organic materials resulting in evolved gases, by means of at least one high temperature burner gas stream by combustion of a fuel with an oxygen-containing gas, to produce said synthesis gas and residual ash, introducing said residual ash from said reactor into a separate melting furnace, vitrifying said residual ash in said melting furnace by combustion of a fuel with an oxygen-containing gas, removing said vitrified ash as a solid frit product, and introducing the combustion gas from said furnace into said reactor.