We have studied the effects of strain on band offsets through a combined photoemission and polarization dependent surface extended x‐ray absorption fine structure (SEXAFS) study of thin Si overlayers on the 4% lattice‐mismatched GaAs (110) substrate. By selectively orienting the heterojunction interface either parallel to or perpendicular to the x‐ray polarization vector, we have independently measured from SEXAFS the Si–Si nearest‐neighbor bond lengths of bonds lying either in the plane or out of the plane of the interface, respectively. The in‐plane bond lengths were larger by a maximum of 2% for our thinnest coverage of 4 monolayers. An ideal pseudomorphic overlayer would have a 4% difference between these bond lengths. We therefore infer a large density of dislocations even in such thin overlayers. From our photoemission measurements we found no resolvable (>0.05 eV) differences in the valence‐band discontinuity between Si overlayers which were either crystalline and 2% anisotropically strained, cryst...