The high-temperature stability of the single crystalline piezoelec-tric material langasite and associated transport phenomena such as the diffusion of the constituents gallium and oxygen are investi-gated. Small structures remain their shape upon annealing at 1350°C for 24 h. The transport phenomena are in accordance with the defect model of langasite. In particular, oxygen is found to be the dominant ionic charge carrier. A newly developed concept based on monolithic structures in langasite is realized by local dop-ing with praseodymium, strontium and niobium. Those elements either increase the conductivity or modify the rate of wet chemical etching. In order to demonstrate the feasibility of monolithic elec-trodes, the operation of locally Sr-doped bulk acoustic resonators is presented. Further, the correlation of electromechanical properties and transport processes is investigated using langasite bulk acous-tic resonators. Doping by niobium lowers e. g. the total loss at high temperatures.