We demonstrate synthesis of freestanding water-soluble indium oxide nanocrystals (In2O3 NCs) by ligand exchange to β-alanine nitric acid (Ala·HNO3) and its application for active channel layer in thin film transistors (TFTs), with investigation of the effect of curing temperatures on the TFT properties in terms of thermal behaviour of the ligand molecules at 150, 300, and 350 °C. After ligand exchange from long alkyl ligand (myristic acid, MA) to short Ala·HNO3, the mobility of NC TFTs cured at 150 °C increased by over 1 order of magnitude, from 1.3 × 10−4 cm2V-1s−1 to 4.5 × 10−3 cm2V-1s−1, due to enhanced tunnelling rate (Γ) between adjective NCs. Higher curing temperatures such as 300 and 350 °C, inducing thermal decomposition of the organic ligands, led to further enhancement of the mobility, particularly up to 2.2 cm2V-1s−1 for the In2O3 NC-Ala·HNO3 TFT cured at 350 °C. It is also found that the ligand exchange of In2O3 NC in acidic condition (e.g. HNO3) would be simple and effective to reduce the surface defects by surface etching, which may lead to better device performances.