Photoemission spectromicroscopy data on Si-GaSe with 0.2 mu m lateral resolution revealed laterally inhomogeneous interface Se-Si chemical reactions. The local Si 2p fits agrees with interface Si selenide parameters; the Se 3d peaks indicate a Si-selenide component; the Ga 3d peaks exhibit a metallic component whose intensity increases with Si coverage. This local interface reaction is related to lateral changes in the band lineup. (C) 1998 American Institute of Physics. [S0003-6951(98)02839-3].