Abstract: A sputtering target assembly composed of a sputtering target and a backing plate with or without an insert or inserts interposed therebetween as necessary characterized by having solid-phase bonded interface accompanied with no appreciable thermal diffusion layer and by said sputtering target substantially maintaining the quality characteristics including metallurgical characteristics and properties that the sputtering target had before it was bonded to the backing plate intact. The sputtering target assembly is obtained by solid-phase bonding the target and backing plate, with or without one or more insert sandwiched therebetween, at a low temperature and a low pressure under a vacuum. The solid-phase bonded interface gives reliable bonds of a bonded area percentage of 100% without non-bonded portions such as pores. The uniformity of microstructure and crystal orientation etc. of a target material is maintained intact with the suppression of crystal grain growth.