An Au—Sn—Ag-based solder alloy for high temperature use containing Sn, Ag, Au and elements that are inevitably contained owing to manufacture procedure, wherein the Au—Sn—Ag-based solder alloy has a composition adjusted so that a solidus temperature is within a range of 280 to 400° C. with a gap between the solidus temperature and the liquidus temperature being within 40° C. The Au—Ag—Sn-based solder alloy has low cost, and is excellent in solderability, reflow wettability and reliability. The excellent reflow wettability of the Au—Ag—Sn-based solder alloy allows it to be useful in reflow bonding of crystal quartz devices, SAW filters and MEMS.