The lineshapes of the In 4d and As 3d core-levels in InAs(110) have been studied using least squares analysis and the surface core-level shifts are found to be +0.28+or-0.02 and -0.30+or-0.02 eV respectively. Consequently, the surface core-level shifts have now been determined for the entire family of III-V semiconductor surfaces which includes GaX(110) and InX(110), where X=P, As and Sb. It is shown that the quantity Delta E_C- Delta E_A, where Delta E_C is the cation surface core-level shift and Delta E_A is the anion surface core-level shift, exhibits a systematic dependence upon the semiconductor ionicity.