The proper treatment of the electron‐phonon coupling between electrons confined to two dimensions (2‐D) by phonons traveling freely in three dimensions (3‐D) requires special care because phonon heating produces a bottleneck in the rate of transfer of energy from the carriers to the phonons. Because the carriers interact with phonons primarily when the latter are close to the quantum well, the latter should be described, not by plane waves, but by packets adapted to the shape of the carrier confinement. A quasi‐equilibrium technique that retains off‐diagonal elements in the phonon wave‐vector permits an unrestricted treatment of the density operator equation. That in turn leads to a choice of wave packet that comes from solving the integrodifferential equations rather than by imposition. Moreover, if the carrier distribution is assumed in quasi‐equilibrium with a given drift and temperature, the coupled partial differential equations are reduced to coupled ordinary differential equations that can be solve...