A high-speed submount was designed and fabricated for 40 Gb/s electroabsorption modulators(EAMs),and characterized in the chip-level packaging and testing of an EAM device.The Al_2O_3-based submount contains a coplanar waveguide(CPW) for microwave signal feeding and a Ta_2N thin-film resistor for impedance matching of EA modulator.Ti/Cu/Ni/Au metal is introduced as the CPW electrode material,and good contact with Ta_2N thin-film is guaranteed accordingly.Therefore,the typical reflection coefficient of the submount is reduced to be lower than-21 dB up to 40 GHz.As a demonstration,a high-speed EA modulator was packaged by using the high-speed submount,and the small-signal modulation bandwidth was measured to be over 40 GHz.