We have used a simple, analytically solvable model to analyze the characteristic s of dual-gate metal-oxide-semiconductor field-effect transistors (MOSFETs) with 10-nm-scale channel length L. The model assumes ballistic dynamics of 2D electrons in an undoped channel between highly doped source and drain. When applied to silicon n-MOSFETs, calculations show that the voltage gain (necessary for logic applications) drops sharply at L ~ 10 nm, while the conductance modulation remains sufficient for memory applications until L ~ 4 nm.