A gas sensor with planar-type micro-hotplate (MHP) with Si-island was designed and fabricated in this paper. The sensor was fabricated simply by using only three masks for the lithography process. The temperature distribution across the sensitive film was simulated and analyzed using ANSYS. A uniform temperature distribution was obtained after added Si-island. The SnO2 sensitive film was deposited through sol-gel spin-coating method and showed reasonable gas-sensing properties to hydrogen at 300°C.