Only a few experimental techniques permit the determination of inhomogenities in the electron density of a plasma, and even these lose their usefulness near the walls of the plasma container. A microwave surface wave technique using the container boundary as a propagating surface is described. Under the assumption that the plasma is azimuthally symmetric and axially uniform, perturbation relations for the microwave field permit an integral transform to convert phase shifts into radial electron density. This technique applied to a 2‐Torr neon rf‐generated plasma in coaxial geometry indicates an electron density near the inner wall as having a square‐law distance dependence. This is not in accord with the well‐known theoretical models of diffusion‐limited plasmas, but can be explained qualitatively.