It was previously shown that the effective contact potential difference (phi(MS)) in Al-SiO2-Si metal-oxide-serniconductor structures has a "dome-like" shape of distribution over the Al-gate area. In this paper we show that this shape is due to the distribution of the barrier height at the Al-SiO2 interface and that the characteristic shape of phi(MS)(x,y) distribution is reflected in a similar shape of the flat-band voltage V-FB(x,y) distribution over the gate area. As opposed to the Al-SiO2-Si system, we find that in poly-Si-SiO2-Si structures both the phi(MS)(x,y) and the V-FB (x,y) distributions are practically uniform. (C) 2007 Elsevier B.V. All rights reserved.