Current transport in Schottky diodes is examined by solving the Boltzmann equation within the semiconductor. The effect of the metal is taken into account by imposing suitable boundary conditions to the above solution, and it is shown that the usual drift-diffusion equation is not correct in the vicinity of the junction. Generalized transport equations are derived, and the current-voltage characteristic is determined. A thermionic-emission velocity twice as large as that derived in the T-D theory is obtained, in accordance with a previous Monte Carlo simulation of the M-S device.