There are provided are an adhesive composition that keeps storage stability and further gives a cured product wherein metallic bonds are formed in the state that the cured product wets its components and is satisfactorily spread between the components (or parts), thereby turning excellent in adhesive property, electroconductivity, and reliability for mounting such as TCT resistance or high-temperature standing resistance; an electronic-component-mounted substrate using the same; and a semiconductor device. The adhesive composition comprises electroconductive particles (A) and a binder component (B), wherein the electroconductive particles (A) include a metal (a1) having a melting point equal to or higher than the reflow temperature and containing no lead, and a metal (a2) having a melting point lower than the reflow temperature and containing no lead, and the binder component (B) includes a thermosetting resin composition (b1) and an aliphatic dihydroxycarboxylic acid (b2).