A fully differential master-slave track-and-hold amplifier is designed and fabricated in a 210-GHz-fT InP DHBT process. Input bandwidth of 15 GHz, total harmonic distortion lower than -39 dB and a third harmonic rejection greater than 45 dB are measured for 1 GSample/s and 4 dBm single-ended input signal. Time domain measurements demonstrate the performances of dual track-and-hold amplifier for Nyquist, over-sampling and sub-sampling conditions. Design tradeoff for master and slave blocks are presented. Experimental results obtained for different feed-through capacitors (CFF) show the effects of CFF on bandwidth and isolation.