In this paper design of fast arithmetic circuits using GaAs based Feed Through Logic (FTL) family [1] is presented. A modified version of FTL termed Differential FTL (DFTL) is introduced and basic aspects of design methologies using FTL are discussed. A 4-bit ripple-carry adder is designed and its performance is evaluated against other similar reported works in terms of, device count, chip area, delay, clock rate, and power consumption. It is shown how arithmetic circuits based on FTL outperform the evaluated performance. A 4-bit magnitude comparator is designed and performance evaluated against four cascaded 1-bit comparators.