A broadband high-speed high-linearity track-and-hold amplifier (THA) is presented in this paper using 0.18 μm SiGe process. A switched emitter follower track-and-hold (T/H) stage with cascode stage is adopted to achieve high resolution for analog-to-digital conversion. A modified Darlington amplifier with peaking technique is used to enhance the input bandwidth. With a dc power consumption of 94.3 mW, the proposed THA demonstrates a 3-dB input bandwidth from DC to 27 GHz, a maximum spurious-free dynamic range of 45 dB, and a minimum total harmonic distortion of -40 dB. The proposed circuit has potential for high-speed high-dynamic-range applications due to its superior performance.