A thin film transistor, comprising: a gate electrode; a semiconductor overlapping the gate electrode; an insulator disposed between the gate electrode and the semiconductor; and a source electrode and a drain electrode electrically connected to the semiconductor, wherein the insulator comprises a cured material of a composition comprising a product of condensation reaction between a thermal cross-linking agent and a product of hydrolysis and condensation polymerization of a compound represented by Chemical Formula 1: In Chemical Formula 1, R 1, R 2, and R 3 are independently hydrogen, a substituted or unsubstituted C1 to C20 alkyl group, a C1 to C20 alkoxy group, a hydroxyl group, a halogen, a carboxyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, a substituted or unsubstituted C7 to C20 arylalkyl group, a substituted or unsubstituted C1 to C20 heteroalkyl group, a substituted or unsubstituted C2 to C20 heterocycloalkyl group, a substituted or unsubstituted C2 to C20 alkylnyl group, or a combination thereof, provided that at least one of R 1, R 2, and R 3 is a C1 to C20 alkoxy group, a hydroxyl group, a halogen, or a carboxyl group, R 4 is hydrogen, or a C1 to C20 alkyl group, L 1 and L 3 are independently a substituted or unsubstituted C1 to C20 alkylene group, a substituted or unsubstituted C6 to C20 arylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C2 to C20 alkenylenegroup, a substituted or unsubstituted C2 to C20 alkynylene group, or a combination thereof, and L 2 is -O-(C=O)-NR"- or -(C=O)-NR"- (wherein, R" is hydrogen, or a C1 to C6 hydrocarbon radical), and wherein the thermal cross-linking agent is at least one selected from the group consisting of aluminum acetoacetate, zirconium acetoacetate, titanium acetoacetate, magnesium acetoacetate, hafnium acetoacetate, and tin acetoacetate. a gate electrode; a semiconductor overlapping the gate electrode; an insulator disposed between the gate electrode and the semiconductor; and a source electrode and a drain electrode electrically connected to the semiconductor, R 1, R 2, and R 3 are independently hydrogen, a substituted or unsubstituted C1 to C20 alkyl group, a C1 to C20 alkoxy group, a hydroxyl group, a halogen, a carboxyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, a substituted or unsubstituted C7 to C20 arylalkyl group, a substituted or unsubstituted C1 to C20 heteroalkyl group, a substituted or unsubstituted C2 to C20 heterocycloalkyl group, a substituted or unsubstituted C2 to C20 alkylnyl group, or a combination thereof, provided that at least one of R 1, R 2, and R 3 is a C1 to C20 alkoxy group, a hydroxyl group, a halogen, or a carboxyl group, R 4 is hydrogen, or a C1 to C20 alkyl group, L 1 and L 3 are independently a substituted or unsubstituted C1 to C20 alkylene group, a substituted or unsubstituted C6 to C20 arylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C2 to C20 alkenylenegroup, a substituted or unsubstituted C2 to C20 alkynylene group, or a combination thereof, and L 2 is -O-(C=O)-NR"- or -(C=O)-NR"- (wherein, R" is hydrogen, or a C1 to C6 hydrocarbon radical), and wherein the thermal cross-linking agent is at least one selected from the group consisting of aluminum acetoacetate, zirconium acetoacetate, titanium acetoacetate, magnesium acetoacetate, hafnium acetoacetate, and tin acetoacetate.