p -type InGaAsSi heterojunctions were fabricated through a wafer fusion bonding process. The relative band alignment between the two materials at the heterointerface was determined using current-voltage (I-V) measurements and applying thermionic emission-diffusion theory. The valence and conduction band discontinuities for the InGaAsSi interface were determined to be 0.48 and -0.1 eV, respectively, indicating a type-II band alignment. © 2007 American Institute of Physics.