This paper presents the post-annealing effects, caused by rapid thermal annealing (RTA), on amorphous indium gallium zinc oxide (a-IGZO) thin film transistor's (TFT) electrical characteristics, and its contact resistance (R(C)) with thermally grown SiO(2) gate dielectric on silicon wafer substrates. The electrical characteristics of two types of TFTs, one post-annealed and the other not, are compared, and a simple model of the source and drain contacts is applied to estimate the R(C) by a transmission line method (TLM). Consequently, it has been found that the post-annealing does improve the TFT performances; in other words, the saturation mobility (mu(sat)), the on/off current ratio (I(ON/OFF)), and the drain current (I(D)) all increase, and the R(C) and the threshold voltage (V(T)) both decrease. As-fabricated TFTs have the following electrical characteristics; a saturation mobility (p,a) as large as 0.027 cm(2)/V s, I(ON/OFF) Of 103, sub-threshold swing (SS) of 0.49 V/decade, V(T) of 32.51 V, and R(C) of 969 M Omega, and the annealed TFTs have improved electrical characteristics as follows; a mu(sat), of 3.51 cm(2)N 5, I(ON/OFF) of 105, SS of 0.57 V/decade, V(T) of 27.2 V, and R(C) of 847 k Omega. (c) 2010 Elsevier B.V. All rights reserved.