Vacuum-emission and carrier-separation techniques have been used to make the first direct observation of ballistic electron transport in silicon dioxide, and the first direct observation in any material of the interaction of ballistic electrons with single phonons of the lattice. With very thin oxides, total ballistic transport of the electrons is observed for voltages of 1 V dropped across the remaining oxide portion after tunneling. For voltage drops >1 V, a transition from the ballistic to the steady-state regime is seen. Monte Carlo simulations are used to predict the observed experimental behavior including quantum mechanical interference effects and phonon-induced sidebands in the electron distributions. © 1986 The American Physical Society.