A foreground calibration technique for current source mismatch in ultra-high-speed DAC was presented. Two calibration sub-DACs were designed. The calibration currents provided by the two DACs were used to compensate the two components of the current source mismatch. Each calibration DAC had the same temperature characteristics as its corresponding mismatch part. Therefore, the total calibration current could automatically track the temperature changes. The two calibration sub-DACs used two different bias currents to replace different temperatures, and then the calibration number was obtained by the designed calibration algorithm. The calibration scheme could effectively reduce the calibration time and improve the temperature stability of the front calibration. A 16-bit 12 GS/s current-steering D/A converter designed in a standard 65 nm CMOS process validated this calibration technology. The test results show that the SFDR of the DAC reachs 65 dBc at 1 GHz analog output. After calibration, the change rate of DNL is less than 8%, and the change rate of INL is less than 5% in the range of -55 ℃ to 125 ℃. Compared with other similar calibration techniques, this calibration technique could achieve better temperature stability.