This work focuses on the separation and quantification of fixed bulk oxide charge, fixed charge at the dielectric-semiconductor interface and interface state charge components in the Pt/Al2O3/In0.53Ga0.47As metal-oxide-semiconductor (MOS) system. The availability of atomic layer deposited Al2O3 dielectrics over n- and p-type In0.53Ga0.47As with a range of well-controlled thickness values opens up an experimental route for the determination of the interface state density (D-it) independently of the total fixed oxide charge using capacitance-voltage measurements taken at 1 MHz and -50 degrees C. Low temperature forming gas annealing (350 degrees C) significantly reduces the amount of fixed charge. The interface fixed charge is reduced from similar to -8.5 x 10(12) cm(-2) preanneal to similar to 7.4 x 10(11) cm(-2) postanneal and the bulk oxide charge is reduced from similar to 1.4 x 10(19) cm(-3) preanneal to similar to 5 x 10(18) cm(-3) postanneal. The forming gas anneal also has a significant effect on the interface state charge, reducing its density from 1.3 x 10(13) cm(-2) preanneal to 4 x 10(12) cm(-2) postanneal. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3545799] All rights reserved.