The paper describes a fabrication process for convex micro-hotplates (MHPs) using surface micro-machining technology. Surface micro-machining provides simplified process and CMOS compatibility over buck Microelectromechanical Systems (MEMS). The low yield of the latter limits the dimension of the fabricated array while limited sacrificial layer thickness in the former leads to higher power consumption. In this work, 700 °C - 950 °C annealing process was carried out on the 190×190 μm2 MHP with 2.8 μm Polysilicon sacrificial layer. Higher temperature leads to lower tensional stress of the membrane and larger curvature of the released MHP, which further causes higher thermal efficiency. The 950 °C annealed MHP has the largest curvature of 2.438 cm-1 and the highest thermal efficiency of 12.76 °C/mW. The proposed process is used to fabricate a 4×4 tin oxide gas sensor array. Experimental result on the response of the sensor array to Ethanol gas is also illustrated in this paper.