A transistor structure includes a substrate, a source electrode, a drain electrode, a protective layer and a gate electrode. The source electrode and the drain electrode are provided on the substrate. The protective layer is provided on the substrate. The protective layer is provided between the source electrode and the drain electrode. The protective layer includes a SiNx layer and a SiOx layer. The SiOx layer is provided on the substrate, the SiNx layer is provided on the SiOx layer, and a through hole of the protective layer is formed to extend through the SiNx layer and the SiOx layer. The gate electrode is provided in the through hole, and the gate electrode is separated from at least part of the SiOx layer so as to form an air gap therebetween.