We examine the limits in scaling of InP-based bipolar and field effect transistors for increased device bandwidth. With InP-based HBTs, emitter and base contact resistivities and IC thermal resistance are the major limits to increased device bandwidth; devices with 1-1.5 THz simultaneous f_tau and f_max are feasible. Major challenges faced in developing either InGaAs HEMTs having THz cutoff frequencies or InGaAs-channel MOSFETs having drive current consistent with the 22 nm ITRS objectives include the low two-dimensional effective density of states and the high bound state energies in narrow quantum wells.