Graphene is under study as a MOSFET channel material due to its high carrier velocities, ~10<sub>8</sub>cm/sec for electrons and holes. The high carrier velocities even at low kinetic energies are favorable for low operational voltages. Narrow bandgap III-V materials (InSb, InAs and InGaAs, also with peak electron velocities ~10<sub>8</sub>cm/sec) are also candidates for high frequency operation at low bias. In this work, we compare the theoretical performance of graphene and narrow bandgap III-V MOSFETs. Our analysis is carried out for the ballistic transport limit, since future high performance devices will likely have gate lengths near or below the carrier mean free path. Our analysis explicitly accounts for the nonparabolic conduction band in III-V’s. Our results show that graphene is expected to exhibit superior on-current and transconductance. The device performance is examined from three perspectives: average carrier injection velocity v<sub>inj</sub> at the virtual source; sheet charge density (Ns) at the virtual source; and ballistic current. Average velocity: For graphene, v<sub>inj</sub> remains constant at 2vd/π (~6x107 cm/s), regardless of Ns (vd Dirac velocity). For III-V materials, vinj for low carrier densities is determined by (2kT/πm*)1/2 (InSb: 4.6x107 cm/s, In0.47Ga0.53As: 2.7x107cm/sec) and increases with Vgs as the carrier population reaches degeneracy. Due to strong non-parabolicity in III-V’s, vinj depends on channel thickness, and gradually saturates at high Ns, becoming comparable to vinj in graphene. The critical value of Vgs where vinj saturates depends on oxide capacitance, and is near Vgs-Vt=0.5 V for InSb at equivalent oxide thickness (EOT) of 1 nm. Ns at the virtual source: For graphene transistors, charge is confined within the graphene layer, avoiding gate capacitance degradation due to finite centroid depth of the electron wavefunction as occurs in III-Vs. The graphene density of states capacitance also benefits from 2x Dirac point degeneracy. Sheet charge density in graphene transistors consists of both electron and holes. Although the overall Ns at the virtual source remains constant as Vds varies, sheet electron and hole densities individually change. Higher Vds results in more holes at the virtual source. For charge balance, more electrons must be present, leading to increasing electron density with increasing Vds. For unipolar devices, however, holes are absent; since increasing Vds discourages backward going electrons, electron density decreases with increasing Vds. Ballistic Current: Combination of large Ns and high vinj at all Ns levels leads to higher drain current for graphene. For representative 1nm EOT case, the ballistic current (transconductance) for a graphene transistor is 1.8mA/m (4.3mS/m), compared to 0.44mA/m (1.9mS/m) for In0.47Ga0.53As, 0.48mA/m (2.1mS/m) for InAs and 0.45mA/m (1.9mS/m) for InSb (Vgs-Vt=Vds=0.3V). However, given ambipolar conduction within graphene transistors, devices may not turn off at low gate bias. Circuit design thus must accommodate a limited ON/OFF current ratio.