Ionization of xenon atoms excited to the lowest states in the n=17 and n=20 Stark manifolds at atomically flat Au(111) surfaces and at heavily-doped n-type and p-type Si(100) surfaces having robust native oxide layers is examined over a range of incident angles. Ionization is characterized by resonant surface ionization with contributions from local fields at the surface associated with surface charging or surface inhomogeneities. For oxidized semiconducting surfaces the local fields are a factor of two to three times larger than for conducting surfaces leading to markedly different results.