We have investigated the magnetoresistance of metal-semiconductor hybrid structures at 4.2 K. The devices consisted of polycrystallineAu and an InAs-based heterostructure that hosted a high-mobility two-dimensional electron system. We have varied the electrical parameters and, in particular, the width-to-length ratio W ∕ L of the linear hybrid structures. The recently discovered extraordinary magnetoresistanceeffect is most pronounced for narrow devices with W ∕ L ⩽ 0.05 , consistent with our theoretical prediction. Relative resistance changes with a factor of 1000 are observed at 1 T. To achieve this an interfaceresistance of only 10 − 8 Ω cm 2 is a prerequisite. This can be prepared routinely by in situ cleaved edge overgrowth.