High-resolution synchrotron-radiation photoemission has been used to study Ce/InP(110), Sm/InSb(110), and Ce/CdTe(110) interface formation at room temperature. These systems are all highly reactive, and there are intriguing differences in the details of interface development. For each, disruption starts at very low coverage and is driven by reaction with the anions. For Ce/InP(110) and Sm/InSb(110), In atoms released by metal-anion reaction are dissolved in the Ce and Sm overlayers. For Ce/CdTe(110), there is strong metal-anion bonding and the formation of the maximum valency Ce2Te3 reaction product. Behavior at higher Ce coverages indicates that Ce atoms cluster and do not wet Ce2Te3. Valence-band studies for Ce/InP(110) and Ce/CdTe(110) show the evolution of the Ce 4f states. Comparison of the Ce/InP(110) results for intermediate coverages to those for single-crystal CeP shows similar bonding configuration whereas comparison to CeTe rules out the possibility of such bonding at the interface. The valence bands for Sm overlayers on InSb show contributions from both divalent and trivalent configurations.