A method of fabricating a fin field effect transistor (FinFET) is provided as follows. A fin structure is formed on a substrate. A gate pattern and a source/drain (S/D) electrode are formed on the fin structure. The gate pattern and the S/D electrode are spaced apart from each other. A blocking layer is on the fin structure to cover the gate pattern and the S/D electrode. A sacrificial pattern is formed on the blocking layer and between the gate pattern and S/D electrode. The sacrificial pattern has a first thickness and a first width. A capping layer is formed on the sacrificial layer. An air gap is formed by removing the sacrificial layer through the capping layer. The air gap is formed between the gate pattern and the S/D electrode and has the first thickness and the first width.